CINCINNATI, OH, USA - No.15 seed Elise Mertens scored the second Top 5 win of her career to stun reigning US Open champion Sloane Stephens in straight set and move into the quarterfinals at the Western & Southern Open.

Mertens, who’s making her main draw debut here in Cincinnati, earned her biggest win-by-ranking of her career over World No.3 Stephens, edging through after a hard-fought 7-6(8), 6-2 battle.

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“It’s really awesome to be able to play like this against a player like Sloane, who has a Grand Slam already,” Mertens said afterward. “It gives you confidence.

“I think I played a great match, not too many mistakes. She doesn’t give you free points, so you have to build them yourself. And I’m pretty happy about the way I played today.”

Stephens, last week’s Montreal finalist, got off on the right foot, grabbing an early break to build up a 2-0 lead. Mertens found her range to finally get them back on serve at 4-4, and stayed toe-to-toe with Stephens in the rest of the four consecutive breaks that followed - breaking Stephens both times she served for the set - and sending them into a tiebreak.

The American held three set points but Mertens fought them off time and time again with her powerful forehands, and eventually converted the second set point of her own to steal away the first set.

Mertens’ pace on her shots seemed to be troubling Stephens, and the Belgian got ahead another break at 3-2 in the second. Fully dialled in, she reeled off five games in row to put away the final set and seal her spot into the quarterfinals after an hour and 40 minutes.

Up next, Mertens will take on the No.8 seed Petra Kvitova in the next round - the Czech player took down Kristina Mladenovic 6-4, 6-2 earlier in the day.

“I think she’s a great player, a lefty, and she’s doing really well this year,” Mertens said. “It’s going to be a great match - I’m really looking forward to it.”