NEW YORK, Aug. 29 (Xinhua) -- The 2016 U.S. Open champion Stan Wawrinka beat determined French qualifier 139th-ranked Ugo Humbert in a tough battle on Wednesday to advance to the men's singles third round of 2018 edition of the Grand Slam.

Wawrinka, who missed the U.S. Open 2017 due to two knee surgeries, needed three hours and 21 minutes to prevail 7-6 (7/5), 4-6, 6-3, 7-5.

"I knew it would be a difficult match," said the 33-year-old Wawrinka. "He's a young player and won his first match."

"I'm really happy with the victory," said Wawrinka, who will take on Canadian Milos Raonic in the last 32.

Canada's Raonic, seeded 25th, defeated France's Gilles Simon 6-3, 6-4, 6-4.

"It's never easy to play and move your best when conditions are so tough," said Wawrinka, who was irked to find a shortage of the ice-filled towels players are using to cool off during the changeovers.

On Wednesday, with temperatures hovering around 35 degrees Celcius, the U.S. Open's extreme heat policy was in effect, allowing women a 10-minute heat break before a third set and men the same before a fourth set to give players a chance to cool down.