Williams, Djokovic cruise, Nishikori works late

Serena Williams and Novak Djokovic kept their time in blazing conditions to a bare minimum on Monday as they breezed into the U.S. Open quarter-finals but Eugenie Bouchard's hopes of a maiden grand slam title melted away in the heat.

Djokovic charged past Philipp Kohlschreiber 6-1 7-5 6-4 to set up a blockbuster meeting with longtime rival Andy Murray, who booked his own place in the last eight with a steamy 7-5 7-5 6-4 win over ninth seeded Frenchman Jo-Wilfried Tsonga.

Williams warmed up for her match in the mid-day sun sporting a black dinner jacket over her pink leopard print dress and then turned back the frustrations of a disappointing season at the majors by hammering Estonia's Kaia Kanepi 6-3 6-3.

Gunning for her third consecutive U.S. Open title, Williams made something of a grand slam breakthrough for 2014 by reaching the last eight.

"I finally made a quarter-final this year!" she shouted to the Arthur Ashe Stadium crowd with arms upraised. "Glad to do it in New York."

Swiss third seed Stan Wawrinka, 10th seed Kei Nishikori and twice Australian Open champion Victoria Azarenka avoided the worst of the heat by playing under the evening floodlights but they were still made to sweat for their wins.

No one work harder, or longer, for their victory than Japan's Nishikori, who needed five sets and four hours and 19 minutes to tame fifth seeded Canadian Milos Raonic 4-6 7-6 (4) 6-7 (6) 7-5 6-4.

The marathon contest equaled the latest finishing match ever played at the U.S. Open with the two exhausted players walking off the Arthur Ashe Stadium court at 02:26 AM local time.

DISTRESSING END

With on-court temperatures hovering near 100 degrees Fahrenheit (38 Celsius), it was another day of survival of the fittest at Flushing Meadows and seventh seed Bouchard was simply not up to the challenge.

The 20-year-old Canadian's bid for a fourth consecutive grand slam semi-final appearance came to a distressing end with a 7-6 (2) 6-4 loss to Russian Ekaterina Makarova.

A tense 50-minute opening set played out under the baking sun went to a tie-break and appeared to drain Bouchard.

On serve 3-2 in the second, she called for a medical time out and trainers rushed on to the Louis Armstrong court to rub her arms and legs with bags of ice while checking her blood pressure.

For a moment it seemed Bouchard would not be able to continue as she covered her face and wept.

"I never want to retire from matches no matter what, I was going to play on for sure," said Bouchard.

"I was feeling very light headed and dizzy on the court. You know, just seeing things a little blurry."

After regaining her composure, Bouchard gathered her resolve and returned to action but was quickly broken.

The battling Canadian refused to throw in the towel and immediately broke back.

Makarova, however, stepped up the pressure and in the end Bouchard simply ran out of steam, the 17th seed breaking her again at 5-4 and ending the ordeal with a sizzling winner.

Makarova will next face 16th seed Azarenka, who overcame an inspired challenge from qualifier Aleksandra Krunic 4-6 6-4 6-4 to end the diminutive Serb's magical run to the fourth round.

Next up for Williams is Italian 11th seed Flavia Pennetta, a semi-finalist last year, who advanced with a 7-5 6-2 win against 29th-seeded Australian Casey Dellacqua.

World number ones Williams and Djokovic have moved imperiously through their draws without dropping a set but the Serb, a U.S. Open finalist for the last four years, will be wary of his upcoming showdown with Murray.

Though Murray is seeded eighth after a sub-par season following last year's back surgery, the Scotsman is approaching top form and has some positive memories of playing Wimbledon champion Djokovic in the grand slams.

Murray beat the Serb to win the 2012 U.S. Open and the 2013 Wimbledon for his two grand slam titles.

Wawrinka fought off two set points in the pivotal third set on the way to a 7-5 4-6 7-6(7) 6-2 win over Tommy Robredo and the Australian Open champion was then able to rest up and watch his next opponent, Nishikori, slug it out with Raonic.