MASON, Ohio -- Madison Keys used her forehand to beat Angelique Kerber -- one of her toughest matchups -- and advance to the quarterfinals of the Western & Southern Open on Thursday night between bursts of rain that resulted in hours-long delays.
Keys had lost five straight matches against No. 4 Kerber, but turned to her forehand to rally for a 2-6, 7-6 (3), 6-4 victory. She hit 35 forehand winners, including the match-ending shot for her first Cincinnati quarterfinals.
She's expecting a lot of attention at the US Open, where she reached the final last year and lost to Sloane Stephens -- her best showing in a Grand Slam event.
"I think it's the first time I'm going to have to be someone defending, getting to the finals of a Slam," Keys said. "I have never done it. That's going to be a new experience for me."
Stephens didn't fare so well Thursday, getting upset by Elise Mertens 7-6 (8), 6-2. The third-ranked Stephens couldn't overcome 37 unforced errors that helped Mertens get only her second career win over a top-5 player.
First, three matches held over from the previous night had to be completed. Top-ranked Simona Halep faced the most unusual challenge in the group.
Fresh off her second Rogers Cup title, Halep arrived in Cincinnati looking to extend her momentum toward the US Open. She appeared to aggravate her lower back on a 105 mph serve during the second set against qualifier Ajla Tomljanovic on Wednesday night. After losing the first three games of the final set, she took a medical timeout for treatment.
Halep returned to the court and took control, running off four straight games for a 4-3 lead when rain arrived, stopping her momentum.
Seventeen hours later, she was back on court and needed only five minutes and eight points to complete a 4-6, 6-3, 6-3 win on Thursday afternoon.
"I have learned that I don't have to give up, because anything can happen," she said.
Halep was scheduled to face Ashleigh Barty in the final match of the day, but it was rescheduled for Friday morning when more storms hit Thursday night.
Two other second-round matches had to be completed in addition to Halep's match with Tomljanovic.
Amanda Anisimova beat qualifier Petra Martic 6-4, 6-3 in a match suspended overnight. Fourth-seeded Juan Martin del Potro beat Hyeon Chung 6-2, 6-3, finally completing the second round in late afternoon. The winners faced the challenge of playing essentially two full matches in one day.
Novak Djokovic and defending champion Grigor Dimitrov were tied at a set apiece when the storms halted play Thursday night, with the match ultimately being suspended to Friday. Djokovic has never won a Western & Southern title, the only ATP Masters 1000 championship to elude him.
Djokovic has reached the finals five times and lost every time. Djokovic is trying once again to become the first to win all nine ATP Masters events.
Djokovic and Dimitrov split the first two sets and then headed inside for a long rain delay. Djokovic broke Dimitrov to go up 2-1 in the third set, and more rain prompted play to be called off for the night. They'll resume in the morning.
Roger Federer's match against Leonardo Mayer was postponed until Friday as well, along with several others pushed back by daylong rain that made a mess of the brackets.