Canada's Eugenie Bouchard is out of the U.S. Open.
The Westmount, Que., native lost her fourth-round match 7-6 (2), 6-4 to Ekaterina Makarova on a sweltering Monday afternoon after needing treatment from medical staff midway through the second set.
The 17th-seeded Makarova advanced to the quarter-finals, where she will face the winner of a match between Victoria Azarenka and Aleksandra Kunic.
The defeat prevented Bouchard from reaching at least the semifinals of a fourth grand slam tournament this year.
Play was stopped for about 10 minutes in the second set after Bouchard wasted two break points to fall behind 3-2.
The 20-year-old, who appeared to be overheated, looked in distress as medics took her blood pressure and then rubbed her down with ice bags at her courtside chair.
She was able to resume the match, but immediately lost her serve. Remarkably, she battled back to break Makarova's service and then hold her own to tie the set at 4-4.
But 26-year-old Makarova broke service again to take the match, winning all four points in the final game and punctuating her win with a forehand return down the line.
Bouchard, whose fan following has swelled with her grand slam success this season, was given an ovation as she walked onto court at Louis Armstrong Stadium, the event's second biggest venue.
Her success, which included reaching the Wimbledon final, vaulted her into the top 10 in WTA rankings. She was seeded seventh at the U.S. Open.
Both players opened strong, holding service without surrendering a point, but Bouchard was broken on her next service game with two double faults. Bouchard had a break point in the next game, but Makarova dominated three straight points to take a 3-1 lead.
Makarova was making shots, particularly with a tricky forehand, and held for 4-2 without allowing Bouchard to return a serve.
But Bouchard got on a roll, holding serve with a pair of aces and then winning a challenge en route to a break to tie the set. It was all Makarova in the tiebreak, however.
A telling stat: Bouchard converted only two of 10 break point opportunities in the match.
Makarova shone at the Rogers Cup in Montreal a month ago, where she lost in the semifinals to eventual winner Agnieska Radwanska.
In another match, top-seeded Serena Williams defeated Kaia Kanepi of Estonia, 6-3, 6-3.