A year ago, Ben Shelton was a sophomore at the University of Florida who was ranked No. 569 in the world and on his way to winning the NCAA singles championship last May.

After beating French Open runner-up Casper Ruud in Cincinnati last August, he turned pro ahead of the U.S. Open.

Coming into the Australian Open, the left-hander had earned just under $300,000 in career prize money. But after defeating Australian wildcard and home country favorite Alexei Popyrin, 6-3, 7-6(4), 6-4, Shelton is into the fourth round in his first Australian Open. Ranked No. 89, he could more than double his career earnings with a victory in his next match against fellow American J.J. Wolf. Quarterfinalists will earn $372,956.

“It feels great," Shelton said. "I said on the court that it's a pinch-me moment. Unreal experience out there on the court today with that Aussie crowd. It was a lot of fun to be out there, and I'm happy to be moving on.”

Shelton is one of four American men into the final 16, along with Wolf, Tommy Paul and No. 29 Sebastian Korda, who upset last year’s runner-up, No. 7 Daniil Medvedev. The last time four American men reached the fourth round was 2004.

“It’s a really exciting time for American tennis,” Paul told ESPN’s Pam Shriver after his win.

No American man has won a major since Andy Roddick at the 2003 U.S. Open.

Wolf, who played collegiately at Ohio State and is now ranked No. 67, dispatched fellow American Michael Mmoh, 6-4, 6-1, 6-2, to reach the fourth round in his first Australian Open.

Paul, who is originally from South Jersey and now trains in Florida, crushed fellow American Jenson Brooksby, 6-1, 6-4, 6-3, after Brooksby had upset Ruud in the second round. Brooksby was dealing with a left wrist injury that had to be taped and impacted his two-handed backhand, and also appeared sluggish in his movement. At one stage in the third set, he appeared to be on the brink of tears as he sat in his chair during a crossover.

“I’m really happy with my level, I know every match is going to be tough,” Paul said. “This match the scoreline didn’t look too tough, but the match was. I mean, it was a physical match and it’s always tricky with Brooksby.”

Next up for Paul is No. 24 Roberto Bautisa Agut, who ended Andy Murray’s run, 6-1 6-7(7) 6-3, 6-4, after Murray had won back-to-back five-setters over Matteo Berrettini and Thanasi Kokkinakis. Murray, the 35-year-old Brit with the artificial hip, spent 14 hours, 4 minutes on court during the tournament, but certainly should feel good about his career going forward. Paul is 1-3 against Bautista Agut.

John McEnroe likes Paul to advance over Bautista Agut and then the winner of the Shelton-Wolf matchup to reach the semifinals, where he could meet No. 4 seed and nine-time champion Novak Djokovic. Djokovic advanced over No. 27 Grigor Dimitrov, 7-6(7), 6-3, 6-4, to reach his 15th Australian Open quarterfinal.

“Now he’s really gotten himself in tremendous shape,” McEnroe said of Paul on ESPN. “In my book, winner of this match [with Bautista Agut], semifinals. This is a great opportunity for Paul.”

Unlike Shelton, Wolf and Brooksby, who went to Baylor but never played, Paul went straight into the pros and never played college tennis.

Shelton was coached at Florida by his father, Bryan, who reached a career-high of No. 55 in 1992. Ben Shelton called his dad after the latest victory.

"He was definitely excited,” he said. “It's like 5:40 there, and they have a match today, the team does. So I think I messed up his sleep schedule a little bit. He still has his analytical mind going and talked to me about the things that I did really well today and the few things that I could have done a bit better. So, yeah, he was happy overall."

Shelton hit 34 winners and made just 25 unforced errors against Popyrin, who upset upset Taylor Fritz, the top-ranked American in the first round. He converted two of his eight break points and won 87% of his first-serve points.

“I told myself that I wanted to give myself more of a green light today when I played, not be as hesitant in the middle of the points but really go for my shots a bit more and be okay with some errors and know that it was going to pay off in the long run," Shelton said. “I thought I stuck to that plan today and executed really well.”

Shelton is up to No. 65 in the ATP Live Rankings and will now face another American in Wolf for a spot in the quarterfinals.

"We're good friends, like to joke around a lot, have a lot of locker room banter. So he is a good guy," Shelton said. "Definitely excited to be able to play him, and I think it's a match that the crowd will for sure enjoy."