WATCH: Opelka beats Berrettini with frightening headshot

Reilly Opelka pulled off a straight-sets upset on Tuesday over No. 6 seed Matteo Berrettini to advance in the Western & Southern Open. But what might be equally notable is that he finished it in frightening fashion, launching a knee-buckling serve right at Berrettini's head:

The serve, his 19th ace of the match, gave Opelka the second-set tiebreak and a 6-3, 7-6 (4) win—and earned him a place in his first career ATP Masters 1000 quarterfinal.

Berrettini didn't suffer the only hard-to-swallow match point of the day, though. Dayana Yastremska, trailing to Naomi Osaka, had a match-ending second-serve foot fault called against her by the temporary Hawk-Eye Live system:

"You cannot challenge," the umpire had to inform a disappointed Yastremska.

Osaka didn't find the ending that shocking, as she's seen crazier.

"It was definitely unusual, but I have kind of had weirder endings, so it doesn't really top that scale," she said, explaining that when she was 13 she lost a match point by getting hit with a ball that was flying out. It seems she can relate to Berrettini, though Opelka's serve was definitely in.

In the quarterfinals, Opelka will face the winner of John Isner and Stefanos Tsitsipas, while Osaka will play Anett Kontaveit. Here's to fewer fraught endings as the New York double header continues.