US Open results: Serena Williams advances, Sloane Stephens upset by Anastasija Sevastova

Tennis US Open

Juan Martin del Potro reached the US Open semi-finals for the third time on Tuesday, defeating John Isner 6-7 (5/7), 6-3, 7-6 (7/4), 6-2 and ending American hopes of a first men's champion at the event since 2003.

Encouraged by her home crowd, the world number three threatened a comeback by getting the match back on serve at 4-3 but was then broken again before Sevastova served out.

Sevastova, who avenged last year's quarter-final loss to Stephens in NY to reach her first grand slam semi-final, converted five of her eight break points and saved seven of the nine against her on the Arthur Ashe Stadium court.

Since her maiden Grand Slam triumph, Stephens has reached a second major final at the French Open. Sevastova, forced out of the game by injuries in 2013 before launching a comeback almost two years later, showed some steely resolve, serving it out on her third match-point opportunity. It just was a really tough day.

Sevastova continued to choose her shots properly, Stephens continued to serve below-par and the Latvian obtained the second consecutive break as the American messed up with an ugly double hander that went wide.

"I saw that she was struggling". She plays a little bit different than most girls. "I think that's what happened today", said Stephens, who said she has been suffering from a sinus infection.

Sevastova, the No. 19 seed, played an unbelievable match to leave Williams and Madison Keys as the only two American women remaining.

Stephens beat Sevastova in the same round past 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.

"I could have [lost] in the first round, and that would have been really bad", she said, invoking some colorful imagery in the process.

The popular Argentinian will now attempt to take a step he has not managed since winning his only grand slam title here nine years ago and reach another final. It's always a hard match, but I thought she played solid today.

"There's four more tournaments left".

More than just a three hour, 31 minute marathon, the quarter-final was a test of survival played in suffocating humidity so extreme that officials called a halt to junior matches on the outside courts for more than two hours.