NEW YORK (AP) -- Bothered by the heat and stifling humidity, Eugenie Bouchard felt dizzy and her vision was blurry.

She got her blood pressure checked. Plastic bags filled with ice were rubbed on her shoulders, arms and legs during a second-set medical timeout.

Bouchard tried to carry on, but it was hardly an ideal time to try to win a tennis match. The No. 7-seeded Bouchard became the latest top woman to bow out at this surprise-filled U.S. Open, beaten 7-6 (2), 6-4 Monday by 17th-seeded Ekaterina Makarova of Russia in the fourth round.

It ended Bouchard's streak of making at least the semifinals at each Grand Slam tournament this year. That included a runner-up finish at Wimbledon in July; the 20-year-old Canadian is only 4-4 since then.

''I definitely felt a lot of outside expectations and pressure to win matches. I felt more like it's normal if I win and it's a bit more of a disaster when I lose,'' Bouchard said. ''But that's something that I need to block out.''

In muggy air, with the temperature in the high 80s (above 30 Celsius), Bouchard began having trouble from the middle of the first set and was checked on by a trainer during the changeover after the second set's fifth game. During that delay, Makarova cooled down by putting ice bags on herself.

Asked what went through her mind during Bouchard's medical break, Makarova smiled.

''Well, actually, I thought, `Thanks,' because I also was tired,'' Makarova said with a smile. ''It was really (helpful) for me also.''

It's not the first time Bouchard has been affected by heat, saying it happened at last year's U.S. Open, too, and as a junior at the Australian Open.

''Once in a while, I get a little bit light-headed,'' Bouchard said. ''That's what happens.''

Her exit means that for the first time since 1977, eight women will have filled the eight finalist slots at a season's Grand Slam tournaments.

Li Na beat Dominika Cibulkova at the Australian Open in January; Li didn't even enter the U.S. Open because of a knee injury, while Cibulkova was stunned by 15-year-old American CiCi Bellis in the first round.

Maria Sharapova edged Simona Halep at the French Open in June; Sharapova lost to Caroline Wozniacki in the fourth round in New York, and Halep went out in the third round against qualifier Mirjana Lucic-Baroni.

Petra Kvitova defeated Bouchard at Wimbledon; Kvitova departed in the third round in Flushing Meadows against 145th-ranked qualifier Aleksandra Krunic, who had a chance to pull off another shocker Monday night against two-time major champion Victoria Azarenka.

While Makarova is into the U.S. Open quarterfinals for the second year in a row, Bouchard's early-for-her major exit certainly fits with the way things have gone the past eight days. Of the top 10 seeded women, only two remain: No. 1 Serena Williams and No. 10 Wozniacki.

The top-seeded man, Novak Djokovic, played mostly mistake-free tennis, making only 19 unforced errors and facing only two break points - both saved - in a 6-1, 7-5, 6-4 victory over 22nd-seeded Philipp Kohlschreiber of Germany.

Djokovic, the 2011 U.S. Open champion, earned a spot in the quarterfinals at the U.S. Open for the eighth year in a row - and at a 22nd consecutive Grand Slam tournament overall. The last time Djokovic was eliminated before the quarterfinals at a major was a third-round loss to Kohlschreiber at the 2009 French Open.

Djokovic now meets two-time major champion Andy Murray, who got past No. 9 Jo-Wilfried Tsonga 7-5, 7-5, 6-4.

In fourth-round men's matches Monday night, No. 3 Stan Wawrinka brushed off a tumble into the stands and beat No. 16 Tommy Robredo 7-5, 4-6, 7-6 (7), 6-2, and No. 5 Milos Raonic played No. 10 Kei Nishikori.

Williams got to her first Grand Slam quarterfinal of 2014 by overwhelming 50th-ranked Kaia Kanepi of Estonia 6-3, 6-3 Monday. Williams has lost 17 games all told - the eighth time she's made it to the U.S. Open quarterfinals dropping that many or fewer.

One of the few glitches came when she tried to serve for the match at 5-2 in the second set, double-faulting twice in a row and getting broken. That, Williams acknowledged, came from feeling a bit of self-imposed pressure after losing in the Australian Open's fourth round, French Open's second round, and Wimbledon's third round.

''I think I felt it in my service game,'' Williams said. ''I'm like, `Can I please make it to a Grand Slam quarters this year?'''

Pursuing a third straight U.S. Open title and 18th Grand Slam championship, Williams has avoided potential matchups against Kvitova, Bouchard and past major champions Ana Ivanovic and Sam Stosur, who beat Williams in the 2011 U.S. Open final.

Williams is 5-0 against her next opponent, No. 11 Flavia Pennetta of Italy.

''Of course, she's better than me, but if I still believe I can beat her,'' Pennetta said, ''maybe if she doesn't have a good day, I can do that.''