When the serve off Jenson Brooksby’s racquet was returned long by No. 2 seed Casper Ruud in the fourth set, Brooksby raised his arms in triumph, walked toward the net, removed his signature baseball cap and shook hands with Ruud.

It was the biggest victory of Brooksby’s career.

The 22-year-old Sacramento native downed Ruud, 6-3, 7-5, 6-7(4), 6-2 in 3 hours, 34 minutes to advance to the third round of the Australian Open.

Brooksby’s victory came about 24 hours after Mackenzie McDonald, a 27-year-old fellow Northern California native, toppled No. 1 seed and defending champion Rafael Nadal in straight sets.

The pair of gigantic upsets by the Americans marks the first time since the 1994 French Open that the top two seeds were ousted by Americans.

Brooksby is ranked 39th and making his Australian Open debut. He was supposed to enter a year ago but came down with COVID-19 the day before he was supposed to fly to Australia.

“Hopefully this is the first of many many good years here to come,” Brooksby said.

Americans J.J. Wolf, Tommy Paul and Ben Shelton also advanced to the third round with wins on Thursday, while No. 16 Frances Tiafoe and No. 29 Sebastian Korda won Wednesday..

“This is quite a tournament for the Americans right now,” former American star James Blake said on ESPN.

Brooksby’s unusual playing style, including his two-handed backhand volleys, and ability to track down opponent’s shots, were trouble for Ruud, who took a medical timeout after the second set.

The biggest problem for Brooksby was closing this one out. He held a trio of match points while trying to serve for the victory at 5-3 in the third set but could not cash any of them in.

After he got broken there by missing a backhand, Brooksby sat down in his changeover seat and yelled at himself: “How?! How?! God!”

Ruud, a 24-year-old Norwegian who reached the French Open and U.S. Open finals in 2022, raced through the end of that set, but Brooksby righted himself in the fourth, jumping out to a 3-0 lead. Brooksby finished things off 1 hour, 15 minutes after his first chance.

Brooksby has shown signs of promise for several years. He enrolled at Baylor to play college tennis, but turned pro after he redshirted his freshman season due to injuries.

At the 2021 U.S. Open, Brooksby took the opening set from world No. 1 Novak Djokovic in their fourth-round encounter before bowing out in four sets. Djokovic gave him some high praise after the electric match in Arthur Ashe Stadium.

“Brooksby is a very young, very talented player,” Djokovic told Brad Gilbert on court. “I told him at the net that the future is ahead of him, definitely. He’s a great player.”

In an interview with me last June, Brooksby seemed to predict that his time was coming.

“I think next year too I’ll do my best to be able to contend and I’ll have learned a lot more to really believe I can do that.”

No American man has won a major since Andy Roddick at the 2001 U.S. Open.

“A lot of Americans doing really well right now, and we’re all pushing each other,” said Brooksby, who now will face Paul. “Just looking forward to the next one.”

There was also a big win for an American woman Thursday: 21-year-old qualifier Katie Volynets defeated No. 9-seeded Veronika Kudermetova of Russia 6-4, 2-6, 6-2.

“I literally have the chills, because the fans here are just incredible,” said Volynets, who reached the third round of a Grand Slam tournament for the first time. “I’ve never played in a stadium this packed and with that many people keeping the energy up for me. It was awesome.”

(The AP contributed)