SAN DIEGO -- A 48-year-old Englishman who waited two decades to earn his first European Tour victory and a PGA Tour pro who hasn't won in more than four years share the 36-hole lead at the 121st U.S. Open at Torrey Pines.

How's that for unpredictable?

There are 18 players within five shots of Richard Bland and Russell Henley and nine more within six. Of the players who made the cut, only nine shots separate the co-leaders from the last 14 above the cut line.

It figures to be a wild weekend with plenty of drama. Here are the top contenders and why they will or won't hoist the U.S. Open Trophy on Sunday:

Richard BlandPosition: Co-leader at 5 under

Why he can win: Maybe if Bland, 48, had been putting on Poa annua greens, like the ones at Torrey Pines, for the past 20 years he'd have more than one victory on the European Tour. On Friday, he had seven birdies in the second round and is No. 2 in shots gained putting (6.61). Bland, who would become only the third Englishman in the last 90 years to win the U.S. Open, is clearly playing with house money and has nothing to lose.

Why he can't win: Bland, the No. 115-ranked player in the world, needed 478 starts on the European Tour to win for the first time at last month's British Masters. His best finish in a major was a tie for 22nd at the 2017 Open Championship. He would be the third-oldest winner of a major. No player ranked outside the top 100 of the Official World Golf Ranking (started in 1986) has won the U.S. Open, according to research by ESPN Stats & Information. Steve Jones was ranked No. 99 when he won in 1996.

Russell HenleyPosition: Co-leader at 5 under

Why he can win: Henley has played nearly flawless golf with only three bogeys over his first 36 holes. The former University of Georgia star moved to 6-under and grabbed the solo lead before bogeying his final hole of the second round to settle for a tie with Bland. History is on Henley's side. Of the previous nine players who held the lead or co-lead in each of the first two rounds of the U.S. Open, five went on to win the tournament.

Why he can't win: Henley, 32, is the No. 63-ranked player in the world and is a three-time winner on tour. But he hasn't won in more than four years and has rarely been in this lofty position in a major. In fact, he has never finished in the top 10 of a major; his best performance at the U.S. Open was a tie for 16th as the co-low amateur in 2010. Can he handle the pressure?

Louis OosthuizenPosition: 4 under, 1 shot back

Why he can win: Few play as well on golf's biggest stages as often as Oosthuizen, who won the 2010 Open Championship and was at least tied for runner-up in the three other majors. He was tied for second in the 2015 U.S. Open and third in 2020. He has been in the spotlight many times.

Why he can't win: Can he close the deal in another major? He's been down this road before. He is one of only three players with top 10s in the 2019 and 2020 U.S. Opens. Rory McIlroy and Xander Schauffele are the others.

Matthew WolffPosition: 4 under, 1 shot back

Why he can win: Wolff's game seems perfect for this setup. Plus, he has the ability to go low. He had eight birdies in the first round -- tied for most in any opening round of the U.S. Open in the past 15 years. He tossed in four more in Friday's second round. Unlike Thursday, Wolff largely avoided big mistakes in the second round, with only one bogey. He also had zero three-putts after having three the day before.

Why he can't win: Wolff probably wasn't supposed to do this well in his first tournament back from a nearly two-month absence to address his mental health. Only eight months ago, Wolff shot a 5-under 65, the lowest ever in a major at Winged Foot, to grab the 54-hole lead in the pandemic-delayed U.S. Open. He shot 75 in the final round and lost to DeChambeau by 6 shots.

Bubba WatsonPosition: 3 under, 2 shots back

Why he can win: Watson, a two-time Masters champion, seems relaxed and confident. He had 11 birdies in the first two rounds, tied for the most he's had through 36 holes in a major. He last did it in the 2010 PGA Championship, which he lost in a playoff to Martin Kaymer.

Why he can't win: His track record in the U.S. Open isn't great. He missed the cut in five of his previous seven starts. Even Watson seemed surprised by his performance here, suggesting that winning the U.S. Open at 42 would be like "winning the lottery without buying a ticket." Will his putter hold up? He isn't regarded as one of the Tour's best performers on the greens, but his stroke has been pretty reliable so far.

Jon RahmPosition: 3 under, 2 shots back

Why he can win: He is arguably the most talented player on tour without a major championship. He would be the first Spaniard to win the U.S. Open, and a victory would come two weeks after he was forced to withdraw from the Memorial with a 6-shot lead after three rounds because of a positive test for COVID-19. He has played exceptionally well at Torrey Pines in the past; he is a combined 51 under in five starts in the Farmers Insurance Open -- the regular PGA Tour event held there -- including a win in 2017.

Why he can't win: He was erratic with the driver on Friday and didn't hit his second fairway until the 13th hole, which caused his temper to flare. He hit only 5 of 14 fairways in the round after hitting twice as many the day before. He needed par-saving putts on Nos. 10, 11 and 12 to stay among the leaders before finding his rhythm on the tee. Will his short game, which has been unreliable at times this season, continue to bail him out if needed?

Xander Schauffele Position: 2 under, 3 shots back

Why he can win: If Schauffele is in contention on Sunday, he'll have the Southern California fans rooting for him. The 27-year-old was born in La Jolla, played much of his high school golf at Torrey Pines and went to college at San Diego State. He had success on the South Course recently, tying for runner-up at the Farmers Insurance Open in January.

Why he can't win: Schauffele has played as well as almost anyone in the majors. He just hasn't gotten over the hump. In his previous 16 career starts in majors, he had top 10s in half of them, including six top 5s. He hasn't finished worse than sixth in his previous four U.S. Opens. Can he finish the deal with everyone rooting for him?

Scottie SchefflerPosition: 1 under, 4 shots back

Why he can win: Scheffler tested positive for COVID-19 and was forced to withdraw only four days before the start of the 2020 U.S. Open. A year later, he's in the mix. He came into Torrey Pines with momentum, after tying for eighth at the PGA Championship and finishing solo third at the Memorial. He's also prolific on Poa annua greens. He leads the field in strokes gained putting this week, needing only 49 putts over the first 36 holes.

Why he can't win: It's asking a lot for the 24-year-old to win his first PGA Tour event at a major. A handful of players have done it -- Charl Schwartzel and Danny Willett at the Masters in 2011 and 2016 were the most recent -- but it's rare.

Bryson DeChambeauPosition: Even par, 5 shots back

Why he can win: He struggled with driving accuracy in the first round, then said the solution came to him in his sleep early Friday morning. The swing change resulted in a four-shot improvement with a second-round 69. He is second in strokes gained from the tee (3.74) and is giving himself plenty of opportunities to make birdies.

Why he can't win: History suggests he won't win. DeChambeau is attempting to become only the third back-to-back winner at the U.S. Open in seven decades -- Brooks Koepka won in 2017 and 2018; Curtis Strange in 1988 and 1989. DeChambeau's swing change wasn't nearly as effective with his irons, which sent him back to the driving range for another long session. Rest assured he's probably sleeping on it, too.

Brooks Koepka Position: Even par, 5 shots back

Why he can win: Even at five shots back, no one else in the field probably believes they're going to win as much as Koepka. Just ask him. He's a four-time majors champion, with two U.S. Open and two PGA Championship titles. Until Friday, he had been in the top 5 of 34 rounds in majors since the start of the 2017 season, which was nearly twice as many as any other player.

Why he can't win: With birdies on two of the first four holes, Koepka looked ready to make his charge toward another major championship win. But then he started spraying his driver everywhere, missing nine of 14 fairways.

Justin ThomasPosition: Even par, 5 shots back

Why he can win: He can grind it out with the best of them, which was the case again on Friday when he fought his way to a 2-under 69 to get back into contention. His iron play was exceptional, hitting 12 of 18 greens. A shaky putter has caused him to have a so-so performance this season, but it has been more reliable here.

Why he can't win: Thomas produced one of the most memorable rounds in U.S. Open history when he fired a 9-under 63 in the third round at Erin Hills in 2017, the lowest round in relation to par in the tournament's history. But that's the only time he was under par in the third round in the four U.S. Opens in which he made the cut.

Rory McIlroyPosition: 1 over, 6 shots back

Why he can win: McIlroy has remained on the fringe of contention without doing anything exceptionally well over the first two rounds. He drove the ball better on Friday than he did on Thursday, however, and believes an alignment change will correct his poor iron shots. He has traditionally played pretty well at Torrey Pines; he was a combined 32 under in his past three starts on the South Course at the Farmers Insurance Open.

Why he can't win: He hasn't won a major since the 2014 PGA Championship. At times, it seems like his game is hanging by a thread. He hit 53.6% of the fairways and 61.1% of greens over the first 36 holes.

Dustin JohnsonPosition: 2 over, 7 shots back

Why he can win: The world No. 1 player, who has been struggling mightily, seemed to find something on his second nine on Friday. He needed to because he was in danger of missing the cut after five bogeys in his first nine holes. He settled down and had just one bogey with three birdies in his final nine to finish at 2-over 73.

Why he can't win: There are too many talented players ahead of DJ on the leaderboard, and he has been too inconsistent off the tee to make a serious charge. He has struggled with his driver and hasn't played very well since winning the Masters in November. He hit only 5 of 14 fairways in the first round, and only 4 of 14 in the second.