MASON, Ohio (AP) — Defending U.S. Open champion Sloane Stephens overcame a thumb injury to cruise into the third round of the Western & Southern Open with a 6-3, 6-2 win over qualifier Tatjana Maria on Wednesday.

Third-seeded Alexander Zverev was less fortunate, slipping to 0-4 in Cincinnati with a 5-7, 6-4, 7-5 second-round loss to Robin Haase.

A trainer applied a bandage to the third-seeded Stephens’ right thumb between the third and fourth games of the second set of this U.S. Open tuneup. The match was Stephens’ first since losing on Sunday to Simona Halep in the finals at Montreal.

Sloane’s semifinal appearance last season is her best Cincinnati finish in six previous appearances.

Ninth-seeded Karolina Pliskova was upset by Aryna Sabalenka, 2-6, 6-3, 7-5 in a second-round match. Fifteenth-seeded Elise Mertens rallied to squeeze past qualifier Rebecca Peterson, 3-6, 6-2, 7-6 (1) into the third round.

Among the men, seventh-seeded Marin Cilic shook off dropping a first-set tiebreaker to get past qualifier Marius Copil, 6-7 (4), 6-4, 6-4 and reach the third round.