Elise Mertens overcame nine double-faults in a haphazard 4-6, 7-5, 7-5 defeat of second seed Simona Halep on Tuesday to move into the Madrid Masters quarter-finals.
The Belgian 13th seed was outpaced in the error list by Halep who struck 10 doubles in the loss which took more than two and a half hours.
Mertens set up a match with fifth seed Aryna Sabalenka – the weekend Stuttgart runner-up to Ash Barty – who administered a 6-1, 6-2 thrashing to American Jessica Pegula in 54 minutes on the back of 25 winners.
Halep had begun the European clay season with last week’s Stuttgart semi-final but was unable to hold onto her lead after winning the first set.
“She played really well and definitely deserved to win, she was stronger in the end,” Halep said.
“I cannot say I played badly, but I had some important mistakes. Sometimes the match can get away from you.
“I had good matches, the tennis was good. I just have to calm down and to see what I have to do better than today.”
Mertens lost serve seven times, outpaced, though, by the eight of second seed Halep, Madrid champion in 2016 and 2017, was knocked out on a second match point.
The Belgian had lost four of five previous matches with former No. 1 Halep, with her only victory in the series coming at the 2018 Doha final.
Main photo:- Elise Mertens celebrates victory in Madrid – by WTATour.com