Turns out Coco Gauff will not win every match she ever plays at Wimbledon. Yes, she’s still unbeaten in singles heading into Monday’s fourth round (9:15 a.m., ESPN), but the 15-year-old American and her partner, Jay Clarke of Britain, lost in the first round of mixed doubles on Saturday.

Gauff and Clark were defeated 6-1, 6-4 by Robert Lindstedt and Jelena Ostapenko.

She looked on the bright side, though.

“I was able to hit a couple of good serves. Got my serve back on track. Practiced some returns against the big-guy serve,” Gauff said. “I think it will help me in the match on Monday.”

And what a match it is: The 313th-ranked teen, who never had played in a Grand Slam’s main draw before, taking on No. 7 seed Simona Halep, a former No. 1 who won the French Open last year. Gauff has already beaten Venus Williams, Magdalena Rybarikova and Polona Hercog to reach the Round of 16.