Novak Djokovic won with ease his singles match at the Cincinnati Open for the first time in two years.
Due to Covid regulations, the 23-time Grand Slam winner was ineligible to compete in the US.
But in May, restrictions for unvaccinated foreign visitors were loosened, allowing him to return to competition.
He won the first set 6-4 against Spain’s Alejandro Davidovich Fokina, who later retired with a back issue.
The 36-year-old Serb’s triumph marked his first singles match in Cincinnati since 2019; however, on Tuesday, he and compatriot Nikola Cacic suffered a loss in doubles when they fell to Britain’s Jamie Murray and New Zealand’s Michael Venus.
“Time flies. Four years seems like it was yesterday. It’s definitely nice to be back,” said the world number two. He will next face Gael Monfils.
“I’ve had some really nice memories from this tournament.
“Winning it in 2018 obviously is a highlight for me; because it was the only Masters I hadn’t won for years. I think I lost four or five finals, mostly to Roger [Federer].
“But I played well in the past and was really glad to have a chance to come back to the States. It’s been two years – I missed it. Some of the biggest tournaments in our sport are played on American soil. I’m just excited to play some tennis.”
Elsewhere, Australian qualifier Max Purcell beat third seed Casper Ruud in three sets for his first victory over a top-10 ranked player.
Purcell, the world number 70, saved six out of seven break points to win 6-4 3-6 6-4 and set up a meeting with three-time Grand Slam winner Stan Wawrinka.
The swiss former world number three continued his return to form with a 6-3 6-4 win over American 16th seed Frances Tiafoe.
The sixth-seeded Jannik Sinner also lost, falling to Serbian Dusan Lajovic 6-4 7-6 (7-1).
Russian third seed Daniil Medvedev moved into the last 16 with a 6-3 6-2 win over Italy’s Lorenzo Musetti.
Medvedev, who won the title in 2019 and advanced to the US Open final, takes on Alexander Zverev of Germany next.
Zverev defeated Yoshihito Nishioka of Japan 7-5, 6-4, and went on to advance with Greek fourth seed Stefanos Tsitsipas and American ninth seed Taylor Fritz.
Tsitsipas will take on Hubert Hurkacz of Poland, who defeated Borna Coric, the defending champion from Croatia.