MASON, Ohio — Andy Murray followed up his second Olympic singles title with a second-round victory Wednesday night in the Western & Southern Open.

The top-seeded Scot beat Argentina's Juan Monaco 6-3, 6-2 to set up a match against South Africa's Kevin Anderson, a 6-2, 6-4 winner over 13th-seeded Richard Gasquet of France.

Murray had trouble adjusting to the balls and called for a trainer to attend to his right back shoulder in the first set. He won nine of the final 11 games.

"There's different balls here, and that's something that's not easy for a tennis player and you have to be careful with that," Murray said. "It totally changes how it feels on the racket and how it feels through your body as well. I served better in the second set. It's just at the start it was a bit sore. I've played a lot of tennis but it's also the ball change."

On Sunday in Rio, Murray beat Spain's Juan Martin del Potro in four sets in the final.

Murray won the hardcourt event in 2008 and 2011 and has reached the quarter-finals in eight of his previous 11 appearances in Cincinnati.

Earlier, Rafael Nadal beat Uruguay's Pablo Cuevas 6-1, 7-6 (4).

Nadal, the third-seeded Spanish star who won the tournament in 2013, also was coming off the Olympics, where he teamed with Marc Lopez to win the doubles title and lost in the bronze medal singles match. Before that, the 30-year-old Nadal had missed two months with an injured left wrist.

"I think I played well," Nadal said. "I think I played a good match against a tough opponent in the first round for me for sure. After coming from Rio and after the marathon that I had, it's a very important victory for me. So I'm very happy."

Nadal avenged a loss to Cuevas in February in Rio de Janeiro in a clay-court event to set up a third-round match against Croatia's Borna Coric, a 7-6 (2), 4-6, 7-6 (6) winner over 14th-seeded Nick Kyrgios of Australia.

Second-seeded Stan Wawrinka of Switzerland also advanced, beating American Jared Donaldson 2-6, 6-3, 6-4.

Also, fourth-seeded Milos Raonic of Canada beat American John Isner 7-6 (5), 7-6 (5); fifth-seeded Kei Nishikori topped Russia's Mikhail Youzhny 6-3, 6-2; sixth-seeded Tomas Berdych of the Czech Republic beat Spain's Marcel Granollers 6-3, 7-6 (4); and seventh-seeded Jo-Wilfried Tsonga of France edged American Reilly Opelka 7-6 (5), 7-6 (3).

Raonic, from Thornhill, Ont., had 12 aces compared to the 20 that Isner produced. The Canadian also had four double faults but won 85 per cent of first serve points.

Defending champion Roger Federer and top-ranked Novak Djokovic are sidelined by injuries.

In women's second-round play, second-seeded Angelique Kerber of Germany beat France's Kristina Mladenovic 6-0, 7-5; third-seeded Simona Halep of Romania edged Germany's Annika Beck 6-3, 6-1; and fourth-seeded Garbine Muguruza of Spain topped American Coco Vandeweghe 7-6 (4), 6-2.

With two-time defending champion Serena Williams forced to withdraw because of an inflamed shoulder, Kerber is in position to take the top spot in the rankings with a tournament victory. Williams has been in the top spot for 183 consecutive weeks.

"It's not on my mind," Kerber said. "If the time is ready and I can reach the No. 1, of course it will be amazing. Still, it's for me still a long, long way to get there."

Halep has won 11 straight matches and her last two tournaments at Bucharest and Montreal.

"I feel confident. I had pretty good tournaments before coming here and I feel my game," Halep said. "I was a little bit nervous before the match because I had two weeks after without matches. Like everyone says, it's tough, the first match of the tournament. Now I'm more relaxed and I'm looking already forward to the next one."

Rain delayed the start of play for 90 minutes. The tournament had 39 singles matches scheduled for Wednesday, making up for weather delays over the first two full days of play. There were eight matches either suspended or postponed from Tuesday that were completed on Wednesday. All eight winners played second matches in the evening.