A MARTINEZ, HOST:

Good morning, I'm A Martinez. This year's U.S. Open is a tournament that keeps on giving. Only a few days after what was likely Serena Williams' last tennis match, the event delivered another memorable moment - the upset of 22-time Grand Slam champ Rafael Nadal by 22nd-ranked American from Hyattsville, Md., Frances Tiafoe, who was in disbelief.

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FRANCES TIAFOE: Yeah, I really don't know what happened.

MARTINEZ: Here's what is happening - of the eight men left at the U.S. Open, six are ranked outside the top 10. It's MORNING EDITION. Transcript provided by NPR, Copyright NPR.