New York - Russia's Andrey Rublev became the second teenager to make the US Open third round on Thursday when he stunned Bulgarian seventh seed Grigor Dimitrov 7-5, 7-6 (7/3), 6-3.
Rublev, just 19 and the world number 53, joins 18-year-old Denis Shapovalov of Canada in the last 32 at a Grand Slam event for the first time.
The teenage number could be boosted later Thursday when 19-year-old Taylor Fritz of the United States tackles Austrian sixth seed Dominic Thiem.
"It's an amazing feeling. I'm very happy to win this match," said Rublev after stunning Cincinnati Masters champion Dimitrov to set-up a clash with Bosnia's Damir Dzumhur for a place in the last 16.
"I was thinking before the match - I have to play my rhythm, my speed, because I know with my speed I can compete with any of the top players and I did it."
In complete contrast, Roger Federer, chasing a record sixth US Open and third major of the year, will face two-time semi-finalist Mikhail Youzhny, in a clash which has a combined age of 71.
Federer boasts a perfect 16-0 record against the former world number eight from Russia, whose ranking has slumped to 101.
Federer, with a 20th Grand Slam title in his sights, needed five sets to get past US teenager Frances Tiafoe in his opening match on Tuesday.
Victory over Youzhny, whom he first played 17 years ago, would give him his 80th win at the tournament.
Top seed Rafael Nadal, the 2010 and 2013 champion, faces Japan's Taro Daniel, the New York-born world number 121.
Nadal and Federer, who have never met in New York, are seeded to face each other in the semi-finals.
Also going through to the last 32 on Thursday was 2009 champion Juan Martín Del Potro, the 24th seeded Argentine who saw off Spanish qualifier Adrian Menendez-Maceiras 6-2, 6-3, 7-6 (7/3).
Karolina Pliskova had to battle back from a set down to make the US Open last-32 on Thursday and hang on to her world number one spot.
The Czech player, who was runner-up in 2016, downed American qualifier Nicole Gibbs 2-6, 6-3, 6-4.
She was joined in the third round by fourth seed Elina Svitolina, one of the pretenders to her top ranking, and French Open champion Jelena Ostapenko.
"It's easier for the other girls to play me as there is more pressure being number one," said Pliskova, who faces either Chinese 27th seed Zhang Shuai or Risa Ozaki of Japan for a place in the last 16.
"Everyone plays their best tennis against me and I felt that today," added Pliskova, who would have lost the number one spot she has held for just six weeks had she lost.
Gibbs, ranked 127 in the world, had only won three matches on tour this year before the US Open, but she raced to a 5-1 lead on her way to pocketing the first set.
Pliskova eventually overpowered the 24-year-old Californian, breaking in the eighth game of the second set and seventh in the decider.
Ukraine's Svitolina reached the last 32 for a third successive year by breezing past Russia's Evgeniya Rodina 6-4, 6-4.
Ostapenko, the 12th-seeded Latvian, made the third round for the first time with a 6-4, 6-4 win against Romania's Sorana Cirstea.
Japan's Naomi Osaka, just 19, followed up her win over defending champion Angelique Kerber with a 6-3, 4-6, 7-5 win over Denisa Allertova of the Czech Republic.
At the start of the day's play, four of the top 10 women seeds had been knocked out - Simona Halep, Caroline Wozniacki, defending champion Angelique Kerber and Johanna Konta.
One to survive was Svetlana Kuznetsova, the eighth-seeded 2004 champion.
She faces Japan's Kurumi Nara having saved three match points in her opener against Marketa Vondrousova.