Novak Djokovic got his campaign to win a fourth US Open, and 18th Grand Slam title overall, off to a flying start on Monday by beating Damir Dzumhur 6-1 6-4 6-1 to advance to the second round.
Djokovic broke Dzumhur's serve for a seventh time to seal the win in the first night match on Arthur Ashe Stadium court, which, due to Covid-19, was missing the thousands of rowdy New York tennis fans that usually flock to Queens every year.
After a dominant start, Djokovic struggled in the second set and lost his temper even after closing it out.
"I thought I started very well, a set and a break (up) then things got complicated," a masked Djokovic said in courtside interview.
"I lost my focus, he started missing less and he put some good variety in the game ... he came up with some good shots and it was anybody's game midway through the second set."
In the end Dzumhur, who hails from Bosnia and Herzegovina, had no answer to the world number one's blistering serve and stout defence in a match that lasted just under two hours.
The 28-year-old did not make it easy on himself, committing 41 unforced errors and eight double faults to fall to 0-3 lifetime against Djokovic.
With the win the Serbian, who won his fourth title of the year at the Western & Southern Open on Saturday, improved to 24-0 on the season.
Djokovic's health had been a question coming into Monday's match after he needed treatment on his neck at the Western & Southern Open but he said he had recovered.
"I feel fine, to be honest I did struggle a bit in the semis and final back-to-back but I had 48 hours to recover," said Djokovic, who resigned as head of the ATP's Player Council at the weekend and announced the formation of the Professional Tennis Players Association.
Next up is a second-round meeting with Briton Kyle Edmund, who defeated Alexander Bublik earlier in the day. Djokovic holds a 5-1 advantage in their head-to-head meetings.
With the two other members of the sport's Big Three — Roger Federer and Rafa Nadal — absent from the tournament, Djokovic is a heavy favourite to hoist the trophy and pull within one Grand Slam title of Nadal (19) and two of Federer (20).