U.S. Open: Novak Djokovic earns hard-fought victory

Top seed Novak Djokovic was made to work hard by Spain's Roberto Bautista Agut before he posted a 6-3, 4-6, 6-4, 6-3 win at the U.S. Open on Sunday, moving him into his 26th consecutive grand slam quarter-final.

After Djokovic won an opening-set groundstroke battle with steady accuracy and well chosen forays to the net, Bautista Agut used his big forehand to come back from 4-2 down in the second and win the next four games to level the match.

The world number one smashed his racquet after losing the second set but made better use of its replacement, winning the third following a service break in the fifth game, before raising his performances in the fourth set to claim victory.

"Congratulations to Bautista for hanging in there, for fighting. It was a great match tonight," said the Serb, winner of this year's Australian Open and Wimbledon titles.

The Spaniard unleashed 34 winners, including 22 from the forehand, but came up short in a quest to reach his first grand slam quarter-final.

"He made me work for every point," said Djokovic, who will meet Spain's Feliciano Lopez, who beat Italy's Fabio Fognini 6-3 7-6(5) 6-1, in the quarter-finals.

Defending champ gets through

Defending champion Marin Cilic is also through to the U.S. quarter-finals, taking down determined Frenchman Jeremy Chardy 6-3 2-6 7-6(2) 6-1 to extend his Flushing Meadows win streak to 11 matches.

Coming off a punishing five-setter with Mikhail Kukushkin in a third-round match that lasted four hours, Cilic took a while to find his power game but was unstoppable once he did, the ninth seeded Croat blasting 23 aces past 27th seed Chardy, who had no answer.

"Key today was finding my rhythm on the serve, especially towards the end of the third set," said Cilic. "I was having trouble a little with my movement after I twisted my ankle in the second set. That was causing me a little trouble, but in the end it's pretty good.

"I played really good in the fourth set, really great tennis, so I'm happy about it."

Cilic has found the defence of his title much tougher than winning, at least so far.

In last year's march to the title, Cilic recorded straight set wins over Tomas Berdych in the quarters, Roger Federer in the semi-finals and Kei Nishikori in the final.

This year, with the exception of a straight sets decision over Russian qualifier Evgeny Donskoy, all of Cilic's matches have gone four sets or more.

After splitting the opening two sets, Cilic's power began to show through particularly in the third set tiebreak when he used his big serve to full advantage firing four aces and going up 6-1 before closing out 7-2.

Cilic kept the pressure up, breaking the Frenchman in the fourth set, surging in front 5-0 and then serving out for the match.

First time for Lopez

Feliciano Lopez has reached the U.S. Open quarter-finals for the first time at age 33, with Fabio Fognini unable to recreate the magic from his upset of Rafael Nadal.

The 18th-seeded Lopez beat Fognini 6-3, 7-6 (5), 6-1 on Sunday. He'll next face the winner of the night match between Novak Djokovic and Roberto Bautista Agut.

Fognini, seeded 32nd, had rallied from down two sets and a break to stun Nadal in a match that didn't end until early Saturday morning. The shots that were hitting the line against Nadal were landing out Sunday, with 40 unforced errors to 28 winners.

Fognini called for the trainer to adjust his back and neck during and after the second set, and he also needed an inhaler in the third.

Lopez is in a Grand Slam quarterfinal for the first time since 2011.