Stephens, who was visibly struggling under the sauna-like conditions, simply had no answer for the steady stream of drop shots sent her way by Sevastova, who later said she was not trying to take advantage of the conditions
Defending US Open champion Sloane Stephens was dumped out in the quarter-finals after losing 6-2 6-3 to Latvian 19th seed Anastasija Sevastova in sweltering conditions on Tuesday.
The third-seeded American lacked the swagger she showed through the opening four rounds and wilted in the sun-baked conditions at Flushing Meadows against Sevastova, who became the first Latvian woman to reach the semi-finals of the US Open.
Next up for the 28-year-old is the winner of the evening match between six-times champion Serena Williams and Czech eighth seed Karolina Pliskova.
Sevastova, who avenged last year's quarter-final loss to Stephens in New York to reach her first Grand Slam semi, converted five of her eight break points and saved seven of the nine against her on the Arthur Ashe Stadium court.
By failing to step up her game for the key points, Stephens allowed the match to get away from her quickly and despite a late fightback was in no shape to pull off a comeback.
"Today I just really couldn't get anything to connect. Even when I did have my break opportunities, I just wasn't playing the points well at all," Stephens, who beat Sevastova during a U.S. Open tune-up in Montreal last month, told reporters.
"Mentally, physically, I just wasn't connecting. It just was a really tough day. The heat doesn't make it any more fun."
With temperatures hovering above 32.2°C, and the tournament's extreme heat policy in effect for a second consecutive day, Sevastova broke an error-prone Stephens to go 3-1 ahead and never looked back.
Stephens, who was visibly struggling under the sauna-like conditions, simply had no answer for the steady stream of drop shots sent her way by Sevastova, who later said she was not trying to take advantage of the conditions.
"I saw that she was struggling. I was struggling also a little bit, but I didn't show it that much. But I don't play dropshots when I see the player struggling or bending over, no," Sevastova told reporters.
"I just play them instinctively, and that's how they work, or don't work sometimes."
Sevastova, who retired from tennis in 2013 due to injuries before returning in 2015, nearly let Stephens into the match in the second set as the American twice pulled back on serve at 2-1 and again at 4-3, but the fightback proved short-lived.
Serving for the match, the Latvian raced out to triple match point and although Stephens saved two of them, Sevastova sealed the win when the 25-year-old American pushed a backhand into the net.