John Isner reaches third round of U.S. Open

NEW YORK — Gael Monfils plays tennis as if he is a circus acrobat. He tiptoes, twirls, tumbles, stumbles and always gets up.

His efforts Thursday night, against 13th-seeded American John Isner, weren’t good enough for a victory, but they did earn the Frenchman more support than his U.S. opponent.

After winning the first two sets, and with the cheer of “Monfils, Monfils,” echoing in his head, Isner barely avoided being upset, ending the match with an emphatic volley and winning, 7-5, 6-2, 4-6, 7-6 (4). The difference might have been Isner’s 23 aces.

The crowd in Louis Armstrong Stadium would sometimes cheer service faults by Isner and stand and cheer wildly for the showy shots from Monfils, who seemed down and out after a couple of his falls.

Isner’s ears may still be ringing with the chants for his opponent, but he doesn’t mind.

“I’m so ecstatic now to be in the third round,” Isner said. “I knew playing against Gael the atmosphere was going to be very electric and that’s what it was. I hope you guys watching had a lot of fun.”

Earlier in the day, two players who have nine U.S. Opens and 33 Grand Slam titles between them, Roger Federer and Serena Williams, won second-round matches with ease.

Williams took a tumble in her 6-3, 6-0 victory over Russia’s Galina Voskoboeva and landed on her bottom at the net. But Williams got up laughing and said she was unhurt.

Federer was a little smoother. He was in that Federer mode in which it seems he is gliding around the court on roller skates, sliding to every ball and making magical shots in his 6-3, 6-2, 6-1 win over Carlos Berlocq of Argentina.

Neither Voskoboeva nor Berlocq should be mistaken for players who should have offered much resistance to two of the best ever. But Williams and Federer are at that age, that post-30 period, when bad things can happen suddenly.

All of the tennis world and anyone who has tickets for the men’s quarterfinals are hoping Federer keeps this form.

The former No. 1 and the man who holds more Grand Slam titles than anyone in history is seeded only seventh here and is slated to meet No. 2 Rafael Nadal in the quarterfinals if form holds. Nadal and Federer have played 31 times but never at the U.S. Open.

Nadal did his part, moving on by dominating Rogerio Dutra Silva of Brazil, 6-2, 6-1, 6-0. Nadal was dressed all in gray, but his game was bright and sprightly.

It’s harder to imagine Williams being in danger until the final, where she is expected to have a rematch with No. 2 Victoria Azarenka, who beat Canadian Aleksandra Wozniak, 6-3, 6-1.

Thursday was one of those days here that can befuddle players. The wind kicked up and knocked the tennis balls around in the air. “I had to be a little cautious,” Williams said. “Just natural, taking into consideration the wind.”

Federer also acknowledged the breeziness but he said, “It was pretty straightforward for me. I hit the ball better than I hit it in the first round. And I think the wind calmed down a little after the Serena match.”

There was a big upset on the women’s side. No. 4-seeded Sara Errani of Italy was beaten by countrywoman Flavia Pennetta, 6-3, 6-1, then broke down in tears and spoke of the pressure she felt being seeded so high.

“The pressure makes everything difficult for me,” Errani said. “I have never been like this. I have never been in this situation. Now you are there and the people playing against you have no pressure and you have a lot of pressure.

“I’m not that kind of player that can go there and make an ace and winner. For me, I have to go out and fight. I feel I am not fighting good with too much pressure. I don’t want to go on the court. I don’t want to go play.”

Caroline Wozniacki, seeded sixth and a finalist here in 2009 and twice a semifinalist, won her second-round match easily, 6-1, 6-2 over Chanelle Scheepers of South Africa.

Nebraska’s Jack Sock, 20, who reached the third round here last year, did it again Thursday with a hard-fought 7-6 (3), 1-6, 7-5, 6-2 win over Maximo Gonzalez of Argentina.

While the buzz of the tournament so far has been created by young American women — such as Christina McHale, who won her second-round match over Elina Svitolina of Ukraine; 17-year-old Victoria Duval, who had upset 11th-seeded Samantha Stosur in the first round before losing Thursday night to Daniela Hantuchova; and 23-year-old Alison Riske, who upset 28th-seeded Mona Barthel of Germany — Sock looks ready to make an American men’s mark too.

Californian Sam Querrey was the opposite, passive and unaggressive. Querrey, seeded 26th, was upset by clay-courter Adrian Mannarino of France, 7-6, (4), 7-6 (4), 6-7 (5), 6-4 and lost a chance to play Federer in the third round.

diane.pucin@latimes.com

Twitter: @mepucin