Rafael Nadal faced his stiffest challenge yet at the U.S. Open but raised his game to beat Marin Cilic 6-3, 3-6, 6-1, 6-2 in New York and continue his quest for a fourth flushing meadows title.

Watched by friend Tiger Woods, the second-seeded Spaniard was in cruise control as he took the first set behind some superb serving and stout defence but the big-hitting Croatian battled back to snatch the second.

That was as good as it would get for Cilic, however, the momentum shifting decisively in Nadal's favour when he jumped in the air to hit a spectacular backhand smash that electrified the crowd.

Cilic would double fault later in the game to give Nadal a 3-1 lead and he would never threaten again on a hot and humid night in New York.

In the last match of the day, Canadaian teenager Bianca Andreescu battled past American qualifier Taylor Townsend 6-1, 4-6, 6-2 to set up a quarter-final clash with Belgium's Elise Mertens today.

Meanwhile, in women's category, defending champion Naomi Osaka was knocked out of the US Open, losing 7-5 6-4 to Switzerland's Belinda Bencic in the last 16.

Osaka, 21, was broken late in the opening set and then again in the fifth game of the second under the Arthur Ashe stadium roof at flushing meadows.

Japan's Osaka will lose her world number one ranking, with Ashleigh Barty of Australia to return to the top spot.

Bencic, the 13th seed, will play Donna Vekic in the quarter-finals.