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Andy Murray ran down every shot in the afternoon heat, his troublesome left knee holding up fine.

Murray, Novak Djokovic and Roger Federer won their opening matches in straight sets Wednesday at the Western & Southern Open, getting accustomed to the heat after spending the past two weeks in London and Canada.

For Murray, it was a chance to gauge how his left knee was doing. He won an Olympic gold medal by beating Federer on the grass at Wimbledon, then dropped out of the Rogers Cup in Toronto last week because his knee got sore in the transition to hard courts.

No problem for the defending Cincinnati champion. He beat Sam Querrey 6-2, 6-4, facing only two break points all match.

"It felt fine," Murray said. "I moved well today. It still was giving me a little bit of trouble in practice for a couple of days before the tournament, but it felt fine, much better on the court today. I moved well, so I'm hoping it won't be a problem."

Djokovic got the bronze medal at the Olympics in London, then won the Rogers Cup on Sunday night. He was a little off in his opening set on a court baked in sunshine and 86-degree heat, before pulling away from Andreas Seppi of Italy 7-6 (4), 6-2.

"Sometimes, it's really hard to try to stay fit for every single tournament and try to perform your best," Djokovic said. "I mean, in the last three, four weeks, I have changed three different cities, places, surfaces, conditions. I'm still trying to figure out where I am."

Federer had no trouble in his evening match against Russia's Alex Bogomolov, winning 6-3, 6-2 in exactly one hour. He served 12 aces and didn't face a break point until the final game of the match.

Federer skipped the Rogers Cup, so it was his first match back on a hard court.

"It's nice to be back on the hard courts," Federer said. "I served really well. He struggled to get into some rallies."

On the women's side, top-seeded Agnieszka Radwanska of Poland advanced to the third round with a 6-4, 6-3 victory over Sofia Arvidsson of Sweden. Venus Williams moved on with her second three-set victory in two days.

Williams won the gold medal in doubles with her sister in London and arrived for the tournament in suburban Cincinnati upbeat. She needed three sets and 2 hours, 23 minutes to win her opening match Tuesday, then followed it with a 2-6, 6-3, 6-2 victory over Russia's Chanelle Scheepers in the afternoon heat that lasted an hour and 46 minutes.

After Scheepers' long return ended it, Williams feebly raised her arm in celebration, walked slowly to the net to shake hands, and sat down and rubbed her forehead with both hands.

It was that kind of a day.

"It was a tough match today," she said. "I wasn't necessarily at my best, but I won anyway. Honestly, that makes me feel good and more relaxed and more comfortable going into tomorrow's match, because I faced some tough players and tough moments and came through."

Radwanska, who received a first-round bye, opened the day on center court and felt a little rusty.

"The first match is always more difficult, with the different balls and conditions," she said. "I was happy to get through it, especially since it was very hot. Hopefully, I'll better (Thursday)."

Radwanska, who lost to Serena Williams in the Wimbledon final and is ranked No. 3 in the world, will meet Sloane Stephens of the United States, who got into the tournament as a wild card.

"I'll just go out and play my game," Stephens said, adding with a smile, "I'm not going to tell you how I'm going to play, because she'll probably read this and know how to play."

In men's action, 10th-seeded Mardy Fish of the United States advanced to the third round by defeating Carlos Berlocq of Argentina 6-3, 6-1. Serbian Victor Troicki moved on to the third round with a 6-2, 6-0 win over Australian Lleyton Hewitt.

Fish was happy to advance relatively easily against an unfamiliar opponent while still working back into form after a surgical procedure to correct a heart condition in May.

"It was nice to get on and off quickly, especially with a win," said Fish, who'd never played Berlocq in singles. "You also can get on and off quickly with a loss. It's somewhat tricky. You never know what to expect. I played as well today as I have all summer."