Third seed Roger Federer overcame physical aches and pains to beat Carlos Berlocq 6-3 6-4 to reach the third round of the Italian Open.
Spain's Rafael Nadal, seeded second, also progressed with a 6-1 7-5 victory over Germany's Florian Mayer.
Top women's seed Victoria Azarenka, of Belarus, beat Israeli Shahar Peer 6-1 6-2 but then withdrew from the tournament with a shoulder injury.
British number one Andy Murray faces France's Richard Gasquet on Thursday.
Their third-round match is third up on the Suppertennis Arena court, with the first match at 10:00 BST.
Azarenka's withdrawal, with 10 days to go until the French Open, came as a surprise as she had shown no signs of the injury during her win over Peer. This tournament is the last major warm-up for the French Open.
The Belarussian's decision to withdraw means her scheduled opponent, Dominika Cibulkova of Slovakia, advances to the quarter-finals.
Federer, winner of the Madrid Masters last weekend, only decided to play after completing his practice session on Wednesday morning.
After setting up a clash with Juan Carlos Ferrero, the Swiss said: "I wanted to see how I felt and make sure that I didn't have anything major because we're ahead of a long summer.
"If this was the last tournament of the season it would be no problem. But as this is the beginning of many tournaments in a row, potentially a lot of five-setters in a row, I need to make sure I make good decisions, so I go round-by-round.
"I'm happy that I felt OK out there today."
Seventh seed Tomas Berdych saw off Lukas Kubot 6-4 6-1 but Janko Tipsarevic, ranked eighth, was the biggest men's seed to fall after losing 6-3 6-1 to Stanislas Wawrinka.
In the women's event, Venus Williams beat Ekaterina Makarova 7-6 (9-7) 6-1, while her sister Serena saw off Nadia Petrova 4-6 6-2 6-3.
But big seeds Agnieszka Radwanska and Caroline Wozniacki both lost.
Third seed Radwanska was beaten 6-4 4-6 6-1 by Petra Cetkovska, while sixth seed Wozniacki retired injured against Anabel Medina Garrigues who won6-4 4-0.
Serena Williams appeared to struggle with her back at times.
"Everyone has aches and pains here and there and today I felt it a lot because I have been playing a lot and practising even more," she said. "Hopefully I'll be better by tomorrow."