NEW YORK – Rafa 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 on Monday and continue his quest for a fourth Flushing Meadows title.

The second-seeded Spaniard was in cruise control as he took the first set behind some superb serving and stout defense 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 favor when he jumped in the air to hit a spectacular overhead 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, with Tiger Woods among the star-studded crowd at Arthur Ashe Stadium cheering on the Spaniard.

“It means a lot to me to have him supporting,” said Nadal.

“He’s an amazing inspiration, all the things that he accomplish in sport, the way that he managed to keep fighting that hard.”

Nadal fired a forehand winner on match point to seal the victory and make his 40th quarterfinal at a Grand Slam event.

“For some moments in the second set I felt there was too many points in his hands,” said Nadal.

“He was pushing me back ... after (the) second set I thought something needed to change.”

The 33-year-old has had a relatively stress-free time at the tournament so far, dropping just one set and getting a walkover in the second round.

Next up for the 18-time Grand Slam champion is a meeting with Argentine Diego Schwartzman, who toppled Alexander Zverev in their round of 16 clash earlier in the day.

The diminutive Argentine has faced Nadal seven times and lost every meeting but has proven a difficult test in the slams, forcing the Spaniard to go four tough sets at the 2018 Australian and French Opens.

“He is one of the most talented players on our tour,” said Nadal, who sometimes trains with Schwartzman. “He has everything, amazing control, amazing speed."

Nadal is on a collision course with third seed Roger Federer and could meet his old rival in Sunday’s final if both players advance. Federer faces Grigor Dimitrov in the quarters on Tuesday.

Bencic upsets top seed Osaka

Naomi Osaka was upset 7-5, 6-4 by Belinda Bencic at the U.S. Open on Monday as the Japanese lost her grip on both her title and No. 1 rank while the Swiss reached the quarterfinals at Flushing Meadows for the second time.

Bencic got off to a bright start on a rainy day in New York, breaking the world number one under the closed roof of Arthur Ashe Stadium, and her superior serving carried the day as she won 82% of her first serve points.

Momentum swung firmly in the 22-year-old Bencic’s direction in the second set when Osaka double faulted to hand the 13th seed a 3-2 lead and the top-seeded Japanese, who appeared to struggle with a troublesome left knee, was unable to recover.

Bencic improved to 3-0 this year against the 21-year-old Osaka, who came through an emotional straight sets win over 15-year-old American Coco Gauff in the third round on Saturday.

Osaka’s defeat means Australia’s Ash Barty, who lost in straight sets to China’s Wang Qiang in the fourth round on Sunday, will regain the world number one spot from the Japanese.

Osaka said that although she was disappointed with Monday’s result she still considered her trip to New York a success.

“Right now, I have this feeling of sadness, but I also feel like I have learned so much during this tournament,” she told reporters. “The steps that I have taken as a person have been much greater than I would imagine at this point.

“So I hope that I can keep growing. I know that if I keep working hard, then of course I’ll have better results.”