Roger Federer eased through to the third round of the Western & Southern Open with a comfortable victory over Juan Martin del Potro.
The world number three lost to the Argentine in the 2009 US Open final, but there was little danger of a repeat in Ohio as Federer won 6-3 7-5.
In the women's event, Serena Williams and Maria Sharapova made it through to round three with straight-set wins.
Britain's Andy Murray plays his opener against David Nalbandian on Wednesday.
Federer dominated the first set against Del Potro, but the Argentine fought back in a closer second set which went with serve until the Swiss broke to go 6-5 up and then went on to close out the match.
"I don't think I really allowed Juan Martin to be able to play the game he usually plays," said Federer.
"It's quick conditions, so you're never going to maybe find the rhythm like you would on a slower court. But I was able to mix it up well, I served well, and did all the right things tonight."
Del Potro took comfort from the fact that the wrist injury which saw his miss most of 2010 appears to have healed completely.
"I'm much better than I expected to be at this stage. I don't have any pain, no dangerous pain. My wrist is OK and I can play on every surface," said the Argentine.
"It is not easy for me but I'm close to what is my favourite tournament and I will be ready for a fight in New York."
American James Blake will meet Federer in the third round after beating Italy's Fabio Fognini 6-4 6-2.
Wimbledon semi-finalist Jo-Wilfried Tsonga, who retired with an arm injury during his Montreal Masters semi-final against Novak Djokovic last week, defeated Croatia's Marin Cilic 6-3 6-4.
"I didn't play the last two days because of my arm, and at the warm-up I was feeling really good," Tsonga said. "It was a really fluid match. Everything was easy for me today, including my serve."
Williams held off a late fightback from Lucie Hradecka to win her first-round match and continue her excellent run of form.
The American, who swon the Rogers Cup last Sunday, battled to a 6-3 7-6 (7-5) win in one hour 39 minutes.
The 13-time Grand Slam champion is ranked 31 in the world as she continues her comeback from injury and illness.
"I definitely think it's the most fit I've been in general," said Williams. "I've never used skinny and me in the same sentence. Maybe me and thick or me and like, curvy or sexy, but not necessarily skinny."
Williams went a double break up to serve for the set at 5-2 in the second but Hradecka rallied and broke back twice to level before forcing a tie-break.
With the score even at 5-5 in the tie-break, Williams secured the mini-break before serving out to set up a repeat of Sunday's Rogers Cup final against Samantha Stosur.
Sharapova, the fourth seed, eased into round three with a 6-1 6-3 win over Anastasia Rodionova of Australia.
Wimbledon champion Petra Kvitova, fifth seed Li Na and eighth seed Marion Bartoli also recorded victories to join Williams and Sharapova in the last 16.