NEW YORK (AP) -- First, there were four break points squandered, along with an early chance for the lead.
Next, three more wasted.
Pretty soon, Sloane Stephens' run at a U.S. Open repeat was lost too.
The defending champion was eliminated Tuesday, beaten by Anastasija Sevastova 6-2, 6-3 in the quarterfinals.
"I didn't play the big points well, and you don't win matches when you don't take your opportunities," Stephens said.
Stephens beat Sevastova in the same round last year en route to her first Grand Slam title, but she missed numerous chances to grab an early lead in the rematch and could never get back into the match.
Sevastova, the No. 19 seed from Latvia, will play either Serena Williams or 2016 U.S. Open runner-up Karolina Pliskova in her first Grand Slam semifinal.
That's further than it ever appeared Sevastova would get in tennis when she retired in May 2013, her body battered by muscular and back-related injuries. She returned nearly two years later and finally broke through on her third straight appearance in the U.S. Open quarterfinals.
"It was an amazing journey, this three, four years," she said.
Juan Martin del Potro got back to the semifinals for the second straight year, with the 2009 champion beating John Isner 6-7 (5), 6-3, 7-6 (4), 6-2. Isner was trying to become the first American male semifinalist at the U.S. Open since Andy Roddick in 2006.
Three-quarters of Arthur Ashe Stadium was in the sun on another day of more than 90-degree temperatures (32.2 degrees Celsius) in New York, and Stephens seemed to lack some of her usual sideline-to-sideline court coverage in the heat.
Stephens said she had been battling a cold, but her biggest problem Tuesday might have been her serve. The No. 3 seed was broken five times in the 84-minute match.
"Mentally, physically, I just wasn't connecting," Stephens said. "It just was a really tough day. The heat doesn't make it any more fun."
Stephens, one of the best defenders in the game, squandered all seven break-point chances in the first set, missing out a chance for early momentum during a lengthy third game of the match. She couldn't convert four chances to break in that game that lasted 18 points, and Sevastova then quickly broke her for a 3-1 lead.
Stephens then couldn't convert three more chances in the next game, and never got another in the first set.
Her frustration became apparent, whether she was gesturing to her coach, staring in annoyance at deep balls that bounced off the baseline, or just screaming out in general.
"I'm trying!" she responded to a plea from the crowd to pick it up in the second set.
She did eventually get close, breaking Sevastova at love to cut it to 4-3 in the second set. But Sevastova broke right back during another lengthy game, this one lasting 14 points, and soon it was over -- but not before Stephens made a pretty good run at becoming the first repeat champion since Williams won three in a row from 2012-14.
"So the fact that I made it to the quarterfinals and played some really good matches and I just competed as hard as I could, I mean, a lot to be proud of," Stephens said. "And obviously defending a title is very hard, very difficult."
Williams could still give the U.S. at least one women's semifinalist after Stephens won an all-American final four last year. Pliskova is the last player to beat her in Flushing Meadows, a victory in the 2016 semifinals before Williams missed the tournament last year, when she gave birth to her daughter.