The tension mounted and temperatures soared at the U.S. Open as top seed Novak Djokovic and Andy Murray set up a sensational quarter-final, and Serena Williams made a 2014 grand slam breakthrough.
Temperatures neared 90 degrees (32 C) in Flushing Meadows and hovered around 100 (38 C) 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.
World number one Djokovic beat the heat by charging 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 quarter-finals 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 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.
Top-seeded Serena Williams turned back frustrations over a disappointing grand slam season by beating Kaia Kanepi to reach the quarter-finals.
World number one Williams 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 quarter-final 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 semi-finalist 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 semi-finals 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.