Serena Williams has overcome a slow start to beat Karolina Pliskova in straight sets and book a place in the US Open semi-finals for the 12th time.

The six-times champion at Flushing Meadows delivered 13 aces, including one on match point, and hit 34 winners in a 6-4 6-3 victory.

Her last four opponent is Latvian 19th seed Anastasija Sevastova, who recorded a shock win over defending champion Sloane Stephens 6-2 6-3 in stiflingly hot conditions in Tuesday’s earlier quarter-final.

Williams trailed by a break in the opening set and then was a point from going down a double break before she turned things around against the Czech eighth seed.

At one stage Williams won eight straight games to seize the momentum in the one hour, 25 minute contest and move to within two wins of claiming a record-equalling 24th grand slam title.

Pliskova is the last woman to beat Williams at the US Open, eliminating her in the semi-finals two years ago.

Williams missed the US Open a year ago, giving birth to her daughter during the tournament in September 2017.

Stephens, who said she had been dealing with a sinus infection, rued all of her wasted opportunities against Sevastova, most notably the seven break points she failed to convert in the first set.

When someone urged her to raise her level in the second set, Stephens replied, “I’m trying!”

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

“I think that’s what happened today. I didn’t convert.”

Sevastova, who retired in 2013 because of injuries and returned nearly two years later, advanced to her first grand slam semi-final.

“Still long way to go, I think,” she said.

The 28-year-old avenged last year’s quarter-final loss to Stephens in New York, converting five of her eight break point chances.

“I think it was very physical today,” Sevastova said.

“It was tough to play.”