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Jannik Sinner has not lost a game on serve in either of his first two matches at this year's US Open
Phil Cartwright
BBC Sport journalist
US Open 2025
Venue: Flushing Meadows, New York Dates: 24 August-7 September
Coverage: Live radio commentaries across 5 Live Sport and BBC Sounds, plus live text commentaries on the BBC Sport website & app
World number one Jannik Sinner says there is still room for improvement despite recording a 23rd successive match victory in hard-court Grand Slams to reach the US Open third round.
Having lost just four games in a dominant first-round win over Vit Kopriva, defending champion Sinner produced another efficient display against world number 36 Alexei Popyrin.
It was another ominous message to Sinner's rivals - Popyrin, who beat Novak Djokovic in the third round in New York last year, had been seen a potentially tricky opponent for the Italian.
But Sinner broke Popyrin's serve early in each of the three sets and wrapped up a clinical 6-3 6-2 6-2 victory on Arthur Ashe Stadium in just over two hours.
Sinner has not lost a match at a hard-court major since the 2023 US Open, when he lost in the fourth round to Alexander Zverev.
He won the title at Flushing Meadows last year and is the two-time defending Australian Open champion.
Wimbledon champion Sinner said he was unhappy with the way he served against Popyrin, having landed only 51% of his first serves.
"I felt like we both didn't serve great but I was returning very well, especially on the second serve," he said.
"I'm very happy about today. Obviously I'm aiming to improve the serve but, about the rest, I feel quite comfortable."
Sinner will face Denis Shapovalov, the 27th seed from Canada, in the third round as he bids for a third major of the year.
Sinner's ruthlessness was demonstrated midway through the second set when, serving at 3-2 up with a break, he saved three break points to secure an important hold.
In the very next game, Sinner broke to love, quashing any hope of a Popyrin fightback.
There was a similar pattern at the start of set three when Popyrin failed to capitalise from 15-40 on Sinner's serve, and the top seed again made his opponent pay with a break to love in the next game.
Musetti and Rublev reach round three
Russian Andrey Rublev came through a tough four-set encounter with American Tristan Boyer to join Sinner in the third round.
Boyer, ranked 113th in the world, extended the match by taking the third set before 15th seed Rublev completed a 6-3 6-3 5-7 7-6 (7-4) victory .
Rublev's next opponent will be Coleman Wong, who backed up his history-making first-round victory against Aleksandar Kovacevic with a four-set win over Australia's Adam Walton.
Wong's first-round success made him the first male player from Hong Kong to win a Grand Slam singles match in the Open era.
Elsewhere, Italian 10th seed Lorenzo Musetti was a 6-4 6-0 6-2 winner over Belgian veteran David Goffin.