World No. 2 Andy Murray made himself heard at the US Open on Thursday, downing tenacious Spaniard Marcel Granollers in straight sets to reach the third round.

With pounding rain creating a din under the new $150 million roof of the Arthur Ashe stadium, Murray battled through a tense first set to triumph 6-4, 6-1, 6-4.

"We're lucky that we get to play under the roof because otherwise there'd be no tennis," said Murray, whose match went on as all action stopped on the outside courts. "It's good for everyone."

But in the 22,000-seat stadium, the acoustics of the roof are proving problematic, and Murray admitted the echoing noise made things difficult.

"It was tough, you couldn't really hear the ball at all," said Murray, who is trying to become just the fourth man to reach all four Grand Slam finals in the same year.

Juan Martin del Potro, who has undergone four wrist surgeries since lifting the US Open trophy in 2009, closed out the action on Ashe with a 7-6 (7/5), 6-3, 6-2 victory over 19th seeded American Steve Johnson.

Del Potro, ranked 142nd in the world as he battles back from the injuries that nearly cost him his career, is back in the Open as a wildcard after a sparkling run to a silver medal in the Rio Olympics.

Among those who didn't have the luxury of the roof, 2014 finalist Kei Nishikori of Japan waited out a third-set rain delay en route to a 6-4, 4-6, 6-4, 6-3 victory over 20-year-old Russian qualifier Karen Khachanov.

Third-seeded Swiss Stan Wawrinka, a two-time semi-finalist, was also up against a qualifier, advancing with a 6-1, 7-6 (7/4), 7-5 victory over 243rd-ranked Italian Alessandro Giannessi.

Eighth-seeded Austrian Dominic Thiem downed Lithuanian Ricardas Berankis 6-4, 6-3, 6-2 to line up a meeting with Spain's Pablo Carreno-Busta, who rallied from two sets down to beat Serbian Janko Tipsarevic 3-6, 4-6, 6-2, 6-4, 6-4.

Australian Nick Kyrgios, the 14th seed, put on a serving clinic, firing 27 aces and winning 45 of 48 first-serve points in a 7-5, 6-4, 6-4 victory over Argentina's Horacio Zeballos.