NEW YORK, United States (AFP) — Anastasija Sevastova ended Sloane Stephens’s US Open title defence yesterday, toppling the world number three 6-2, 6-3 to reach a first Grand Slam semi-final.

Stephens refused to blame the punishing heat and humidity on Arthur Ashe Stadium, where her inability to convert any of seven break chances in the opening set paved the way for her defeat.

“When you don’t play big points well, the match can get away from you,” she said.

Sevastova, who stepped away from the game for two years in 2013 after a variety of injuries, will face either 23-time major champion Serena Williams or Karolina Pliskova for a place in the final.

With the departure of third-seeded Stephens, eighth-seeded Czech Pliskova is the only top-10 woman left in the draw.

Six-time US Open winner Williams is seeded 17th as she battles for her first Grand Slam title since the birth of daughter Olympia during last year’s tournament.

The US superstar, who can match Australian Margaret Court’s all-time record of 24 major titles with a victory, fired an impressive 18 aces in a three-set victory over hard-hitting Estonian Kaia Kanepi in the fourth round.

Sevastova herself relies on variety more than power, and she caught a slow-moving Stephens with a number of drop shots and drop-shot lob combinations.