MELBOURNE, Australia -- Learner Tien, a 19-year-old qualifier from California, became the youngest American man to reach the Australian Open's third round since Pete Sampras in 1990, upsetting a racket-tossing Daniil Medvedev 6-3, 7-6 (4), 6-7 (8), 1-6, 7-6 (10-7) in a match that began Thursday night and ended in the wee hours of Friday.

The 4-hour, 49-minute contest had a bit of everything, including -- hard to believe -- a six-minute rain delay that interrupted play shortly before 2:30 a.m. with Tien serving at 5-all, 15-all in the fifth set. When they resumed, Medvedev broke and served for the victory at 6-5, but Tien wouldn't cede a thing, broke back, and forced the concluding first-to-10 tiebreaker that he emerged to win shortly before 3 a.m., about two hours after he failed to convert his initial match point.

"Belief is a big thing in succeeding and winning, in general. I always go on the court believing that there's a chance I can win," said Tien, who showed up at his news conference toting a white cardboard box with a pepperoni pizza. "I wasn't trying to think of the match as anything more important than any other match I've ever played. I was just going to go out there, have fun, see what I could do."

As for the postmatch snack, he said, "It was either going to be celebratory or a binge-y, like, cope. It feels better it's more celebratory, for sure."

The outcome was eyebrow-raising because of the wide gulf in experience and accomplishments between the two players at Margaret Court Arena. Tien is ranked 121st and owned a career Grand Slam record of 0-3 before this week; Medvedev was seeded No. 5, won the 2021 US Open and was the runner-up at Melbourne Park in three of the past four years, including 12 months ago.

"It was definitely harder than maybe it could have been, but, whatever," Tien said on court right afterward, then told the crowd: "I really appreciate all you guys staying out here. I know it's late. I have no idea what time it is."

Tien's upset over Medvedev was the biggest upset in the men's draw by betting odds so far, as Tien closed as a +400 underdog, according to ESPN BET odds. However, the biggest upset of this year's tournament so far came on the women's side when Laura Siegemund, a +1100 underdog by ESPN BET odds, took down 5-seed Zheng Qinwen in second-round play.

"I was definitely hoping it wouldn't go to a fifth-set breaker. ... It was definitely harder than maybe it could have been, but, whatever," Tien said, then told the crowd: "I really appreciate all you guys staying out here. I know it's late. I have no idea what time it is."

Because of the time difference, the match ended at about 8 a.m. on Thursday morning back home in California, and he took the microphone to speak directly to his family -- he said he hoped they were tuned in on TV.

"I don't know if my parents are still watching. ... I love you guys. Thank you for always supporting me from across the world," Tien said. "I know you guys wish you could be here. I wish you could be here, too."

The left-handed Tien played fearlessly and almost flawlessly for stretches, surprisingly getting the better of lengthy exchanges at the baseline: Across the first two sets, he won 32 of the 51 points that lasted nine or more strokes, even coming out on top on one that went 45 shots and another that lasted 32.

Tien did not blink until he reached the precipice of by far his most important win, holding a match point in the third-set tiebreaker when he led it 7-6. But Medvedev erased that with a 122 mph ace and eventually converted his third set point at a little past 1 a.m., then easily pushed things to the fifth set.

Medvedev was penalized a point in the third set while showing the same sorts of signs of frustration that led him to destroy a tiny camera hanging in the net by smacking it with his racket during a surprisingly difficult, five-set, first-round win against an opponent ranked 418th.

After getting broken to trail 4-3 in the second set when Tien delivered a lob that landed at a baseline -- not the only time he did that to his 6-foot-6 foe -- Medvedev chucked his equipment toward the sideline, skidding it across the court until it reached an advertising panel near his bench. At other moments of anger, Medvedev hit a ball against the back wall, toppled a camera behind a baseline and punched his racket bag. He also voiced displeasure about being called for two consecutive foot-faults, resulting in a double fault, during the second-set tiebreaker.

This was Medvedev's first tournament of the season -- his wife recently gave birth to their second child -- and he never really displayed his best tennis. As he often does, the 28-year-old Russian shifted tactics in an attempt to change the course of things, pushing forward to the net frequently early in the third set.

Some mistakes by Tien handed over a service break and a 4-3 lead to Medvedev in that set. But Tien broke right back, then held for a 5-4 edge after Medvedev got docked a point.

Tien reached two junior Grand Slam singles finals in 2023, at the Australian Open and US Open, and played one semester of college tennis at Southern California before turning pro that year.

He just turned 19 last month, and now is the youngest man from the United States to get this far at the Australian Open since an 18-year-old Sampras reached the fourth round in 1990. Sampras won the US Open later that year for the first of his 14 Grand Slam titles, a total that ranks fourth among men in tennis history. Tien and Alex Michelsen are the first pair of American men 20 or younger to advance to the third round at a major since 2003, and the first at the Australian Open since 1990.

The Tien-Medvedev match was the latest significant result for a teen in Melbourne this year.

Tien joined Joao Fonseca of Brazil and Martin Landaluce of Spain as the first trio of teenagers to participate in the qualifying rounds and make the men's bracket at a major since Wimbledon in 2017. Then Fonseca, who beat No. 9 Andrey Rublev, and Jakub Mensik of the Czech Republic, who defeated No. 6 Casper Ruud, became the first pair of teens to beat top-10 men at the same Grand Slam tournament since Novak Djokovic and Andy Murray did it at Wimbledon in 2006.

Now Tien makes it three. He called what Fonseca and Mensik did "definitely pretty inspiring."

Information from The Associated Press was used in this report.