NEW YORK (Reuters) - The tension mounted and temperatures soared at the U.S. Open on Monday as top seed Novak Djokovic and Andy Murray set up a sensational quarterfinal, andSerena Williams made a 2014 grand slam breakthrough.
Temperatures neared 90 degrees in Flushing Meadows and hovered around 100 on the hard courts in high humidity that tested players.
The sweltering conditions nearly sent out promising Canadian Eugenie Bouchard as the 20-year-old seventh seed had ice applied to her arms and legs and had her blood pressure checked during her fourth-round match before she was eliminated 7-6(2) 6-4 by Ekaterina Makarova.
Djokovic, ranked No. 1 in the world, beat the heat and charged past 22nd seed Philipp Kohlschreiber of Germany, 6-1, 7-5, 6-4.
"It's important, obviously, in these particular conditions not to get carried away by frustration of heat," said Djokovic. "And especially after long rallies try to get extra breath.
"Obviously, when I won second set I wanted to get the job done in three."
Murray also made straight-sets work out of his clash against Jo-Wilfried Tsonga, posting a 7-5, 7-5, 6-4 victory over the ninth-seeded Frenchman who had beaten him in the quarterfinals at the run-up tournament in Toronto.
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 Wimbledonchampion 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.
Top-seeded Serena Williams turned back frustrations over a disappointing grand slam season by beating Kaia Kanepi to reach the quarterfinals.
Williams, ranked No. 1 in the world, is gunning for her third U.S. Open title in a row but for the moment saw her 6-3, 6-3 victory over the Estonian as an important hurdle after failing to get past the fourth round in this year's other grand slams.
"I finally made a quarterfinal this year!" she shouted to the Arthur Ashe Stadium crowd with arms upraised. "Glad to do it in New York."
Williams will meet Italian 11th seed Flavia Pennetta, a semifinalist last year who advanced with a 7-5, 6-2 win against 29th-seeded Australian Casey Dellacqua.
Russian 17th seed Makarova, a dangerous opponent in the majors, produced another upset with her defeat of Bouchard, who wilted under the punishing conditions after showing her immense promise in reaching semifinals of the year's first three slams.
A tense opening set played under a blazing sun that went to a tie-break and took 50 minutes to decide appeared to drain the Canadian.
During the changeover at 3-2 in the second set, a distressed Bouchard called for a medical time out and trainers rushed onto the baking 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 with her hands and wept.
After regaining her composure, Bouchard gathered her resolve and returned to action but was quickly broken.
The battling Canadian, however, refused to throw in the towel, immediately breaking back to get back on serve.
But Makarova stepped up the pressure and in the end Bouchard ran out of steam, the Russian breaking her again at 5-4 and ending the ordeal with a sizzling winner down the line.
"It was really a tough match, with these conditions," Makarova told the Louis Armstrong Stadium crowd. "We were fighting really hard. It was a great match."
The Russian, who has beaten the likes of Angelique Kerber, Agnieszka Radwanska and Vera Zvonareva in grand slam events when they were ranked among the top seven in the world, will next play either 16th seed Victoria Azarenka or Aleksandra Krunic.
In a later match, Australian Open champion Stan 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 Spain's Tommy Robredoto reach the quarterfinals.
After splitting the first two sets, the third-seeded Swiss trailed 6-4 in the third-set tiebreaker but battled back to win 9-7 and closed out the victory over the Spanish 16th seed in the fourth set.
"It was a really tough battle today. It's always tough to play against him. He is always fighting," said Wawrinka, who showed his competitive fire with a dive into the stands during a point in the tight confines of Louis Armstrong Stadium.
Wawrinka will play either big-serving Canadian Milos Raonic, the fifth seed, or 10th-seeded Kei Nishikori of Japan in the quarterfinals.