Fourth seed Tommy Haas wins six break points without having his serve broken once and cruises past Michael Russell, 6-4, 6-2. (Matthew Stockman/Getty Images)

Mardy Fish played on an ankle that he said was at three-quarters strength. But, everything else was fine. For Fish, it’s a welcome respite. His heart surgeries are in the past, now he’s looking to build confidence.

And that may be the hardest part.

Fish dropped the first set before winning 12 of the last 15 games en route to a 4-6, 6-1, 6-2 win over opening-round foe Bjorn Phau of Germany at the Citi Open at Rock Creek Park’s William H.G. FitzGerald Tennis Center.

He said he hasn’t had a sip of alcohol since undergoing heart surgery early this year and attempts to limit his caffeine and stress. Fish’s doctors told him those three things could trigger more problems for him.

He said his mind can play tricks on him when he’s playing, which in turn deters from his confidence.

“When we’re out there playing, sometimes you can convince yourself that you’re not feeling well or that you’re going to cramp,” Fish said. “Because I don’t have my full confidence back yet, sometimes, when I don’t feel 100 percent I tend to let my mind go into bad places.”

In the last set, Fish remained confident in his serve as it hit 134 mph. In his clinching game, Fish recorded a 129-mph serve that stayed tight to the center line. Fish sealed the match after Phau’s return of his 89-mph second serve went awry to the left side.

After dropping the opening set, Fish maintained control with his quick footwork at the baseline and his ability to scoop out returns. He broke Phau’s serve four times and won six of his own seven break points.

“The field’s certainly weaker because of the Olympics, but there’s still great players,” Fish said. “I could’ve lost tonight, I could lose my next match.”

In men’s doubles, James Blake teamed with Tim Smyczek to win in the opening round, 6-7, 6-3 and a 10-8 tiebreaker, over Scott Lipsky and Santiago Gonzalez. Blake and Smyczek prevailed despite landing just 57 percent of their first serves.

Blake won his first singles match Monday and will meet Marco Chiudinelli on Wednesday.

In women’s singles, Sloane Stephens was blanked in the second set before rebounding for a 6-2, 0-6, 6-1 win over Michelle Larcher de Brito. Stephens’s return was on point in the third set as she won 56 percent of her opponent’s serves.

Earlier in the evening, Tommy Haas continued his successful summer with a 6-4, 6-2 first-round win over Michael Russell.

The fourth seed in the field, Haas said he was prepared for a difficult challenge in the opening round. Russell reached the quarterfinals of his past two tournaments and entered Tuesday after winning a pair of qualification matches.

“I respect his will to keep going,” Haas said. “He’s one of the hardest-working guys on the tour and hard work pays off.”

Although he landed just 60 percent of his first serves, Haas was able to record five aces. Haas controlled his return to capture six break points, without having his serve break once. He fell behind two games to one in the second set before rolling to five consecutive wins.

Earlier this summer, Haas topped Roger Federer in the final of the Gerry Weber Open and later was the runner-up at the German Open in Hamburg.

He said he isn’t sure how much longer he’ll continue to play, but is in his best physical shape in a long time. He hopes to play long enough for his 1-year-old daughter to be able to enjoy his matches.

“My will is still there,” Haas said. “I can still get as nervous as I did 15 years ago, and I still want to win as much as I did 10 years ago. As long as I have that, I think it’s a good sign, because I do care about winning or losing.”