World number one Daniil Medvedev opened his US Open title defence by walloping American Stefan Kozlov 6-2 6-4 6-0 in sweltering conditions on Arthur Ashe Stadium.
The Russian had an inconsistent run-up to Flushing Meadows but was back to top form on the court where he won his maiden grand slam title a year ago, sending across 10 aces and neutralising Kozlov's serve.
The pair traded breaks early in the first set before Medvedev got his motor running, clinching the next four games as Kozlov won fewer than half of his first-serve points.
Kozlov was no match for Medvedev's raw power in the second set. The American scraped his wrist and knee after he dived to retrieve the ball, but ended up falling to the ground heavily in the ninth game that saw Medvedev break him to love.
He called on the trainer to tend to the injuries but Medvedev showed no mercy as he raced through the final set like a bullet train in just 27 minutes to set up a meeting with Frenchman Arthur Rinderknech in the second round.
Medvedev, who defeated Novak Djokovic 12 months ago to lift the trophy, is hoping to draw on his positive memories, saying: "I definitely don't want to forget about them. It’s a little bit extra pressure but mostly I don’t feel it.
"Probably the only pressure is that I know if I’m not going to play good here for whatever reason, people might say, 'Yeah, the defending champion lost’. I know what I have to do."
Andy Murray recorded a straight-sets victory over 24th seed Francisco Cerundolo.
The 35-year-old went into the tournament having only won one match on the North American hardcourts this season and with concerns over persistent cramping, but this proved to be a relatively straightforward outing in the humid conditions.
Argentinian Cerundolo has won the majority of his ranking points on clay and Murray had to grind his way through plenty of long rallies on his way to a 7-5 6-3 6-3 victory, with the only real negative a failure to serve out all three sets.
Dominic Thiem was unable to defend the title he won in 2020 last year because of his long-term wrist injury and his return lasted only one match as he was beaten 7-5 6-1 5-7 6-3 by 12th seed Pablo Carreno Busta.
Sixth seed Felix Auger-Aliassime dropped a set against Swiss qualifier Alexander Ritschard but recovered to win 6-3 6-4 3-6 6-3, while fifth seed Casper Ruud eased to a 6-3 7-5 6-2 victory over Kyle Edmund.
But former champion Stan Wawrinka retired after losing the first two sets to France's Corentin Moutet.
There was a landmark win, meanwhile, for former junior champion Wu Yibing, who became the first man from China to win a main-draw match at a grand slam in the open era with a 6-3 6-4 6-0 victory over Georgia's Nikoloz Basilashvili.
Zhang Zhizhen had looked set to pip him to it only to miss out on seven match points in the third set and go on to lose in five to Tim van Rijthoven, with the Dutch player prevailing 3-6 6-7 (4-7) 7-6 (11-9) 6-1 6-4.
