NEW YORK (Reuters) - Serena Williams has a record-tying 24th career Grand Slam title in reach but will face perhaps her toughest test so far at this year’s U.S. Open when she meets Ukrainian fifth seed Elina Svitolina in the semi-finals on Thursday.

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Williams needed just 44 minutes to complete her rout of China’s Wang Qiang, who was making her Grand Slam quarter-final debut, but she knows a much tougher test awaits if she is to book a spot in Saturday’s final.

The eighth-seeded American has a 4-1 career record against Svitolina but the Ukrainian has not lost a set in New York and beat Williams in straight sets when they last met at the 2016 Rio Olympics.

“Well, she is obviously a fighter. She gets a lot of balls back. She doesn’t make a lot of mistakes,” said Williams “She’s one of those players that does everything really well. So I have to do everything well, too.”

Since returning from maternity leave in 2018, Williams has had three opportunities to draw level with Australian Margaret Court’s Grand Slam record but fell in the last two Wimbledon finals and last year’s U.S. Open final.

Svitolina, who said this week her win in Rio gave her the confidence that she can go toe-to-toe with the game’s best hitters, is tenacious on court and chases down balls with an intensity that could cause trouble for Williams.

“I played some big hitters in this tournament, a lot, and I have to just react quickly with my feet and with my shots, as well,” said Svitolina, whose U.S. Open tune-up included quarter-final berths in San Jose, Toronto and the last 16 in Cincinnati. “Then when I have the opportunity, go for it.”

In the other women’s semi-final, Swiss 13th seed Belinda Bencic, who knocked out 2018 champion Naomi Osaka in the fourth round, will face Canadian 15th seed Bianca Andreescu.

Bencic, who five years ago reached the U.S. Open quarter-finals as a 17-year-old, will be looking to make the most of her run after a string of injuries interrupted her progress.

That it took so long for Bencic to finally reach a Grand Slam semi-final when it had once seemed like such success would be a certainty, she said she never lost faith during the arduous journey even when it seemed most improbable.

“It’s there like a dream always. Even when you are playing bad, you want to come back to this feeling,” said Bencic.

“You want to eventually get the big wins and have these nice feelings. I think that’s the motivation enough to keep going.”