Federer won the Western & Southern Open last year for his unprecedented sixth title at the longtime ATP Tour stop. He got a good start Tuesday by easily handling Bautista Agut, whom he has beaten in straight sets in all four of their matches.
Federer worked out at his home in Switzerland instead of playing in the Rogers Cup last week. He was a little rusty at the outset on Tuesday but got into a rhythm as the match went along. He didn't face a break point during the 1-hour, 9-minute match and lost only three points off his serve in the second set.
"It's been a while since I've had a match," Federer said. "So that's what gets you in a different mood, different thinking. You know, I can switch it on very quickly. I only need literally like 10 minutes to really get ready for the match."
John Isner's summer surge ended with an opening-round loss to friend and doubles partner Sam Querrey, leaving him with some things to work out before the U.S. Open. Querrey was steady throughout a 6-3, 7-6 (3) win over Isner, the first upset on the men's side.
Isner, the No. 11 seed, had won 11 of 13 matches on hard courts this summer, winning the title in Atlanta, reaching the final in Washington and advancing to the quarterfinals in Montreal. He'll rest heading into the Open.
Isner was worn down from the stretch of matches in those three tournaments.
"I have definitely felt better," Isner said. "That's the thing: You put some good weeks together, it can put you in a bit of a deficit the following week. But regardless, it's disappointing to lose."
Querrey improved to 4-1 against Isner. He also beat him in straight sets in the quarterfinals at Memphis this year.
The Americans have teamed up in doubles for at least two tournaments each year since 2008. They had never played each other in the first round of a Masters event.
"It's not that fun, but you know it happens all the time," Querrey said. "It's just part of the game. After in the locker room we talked like nothing happened, so everything is all fine."
The women's bracket lost two players who were hoping for rejuvenating weeks in Cincinnati.
Sharapova withdrew from the Rogers Cup last week because of a strain in her upper right leg. She had hoped to get some matches in Cincinnati to get ready for the U.S. Open, but the leg was still bothering her.
"I have been practicing here the last few days, and I'm just looking at the U.S. Open in, you know, 11 or 12 days," Sharapova said. "It's a tough decision to make, but I think a wise one, in order to give myself the right amount of time to be as healthy as I can be for the Open."
Venus Williams withdrew from her evening match against sixth-seeded Ana Ivanovic because of illness. Since losing to sister Serena at Wimbledon, she has made first-round exits at Istanbul and Toronto and had to withdraw from Cincinnati after one match.
"After warm-ups, I get a feel for how the match might go or how much you can give or you can't give," she said. "I definitely would have liked to have more matches, but I have to use my experience now."
Sloane Stephens got started toward a second championship, beating 10th-seeded Carla Suarez Navarro 6-1, 6-2. She won her first pro title at the Citi Open on Aug. 9 in Washington.
"[You're] always like searching and trying to find that next great moment, and like that was like one Sunday where I had a great moment," said Stephens, a first-round loser at Toronto last week. "Now, I'm like, 'I need another Sunday. Come on.'"