Two-time US Open champion Tracy Austin has said that Serena Williams's semi-final loss to Roberta Vinci is "one of the biggest in the history of tennis".
Williams lost 2-6 6-4 6-4 to the world number 43, who was playing in her first Grand Slam semi-final at the age of 32.
"This is monumental. It's a shocker," Austin told BBC Sport.
"This is one of the biggest upsets in the history of tennis, because of what was on the line.
"Roberta Vinci had a losing record coming into the US Open and somehow got hot.
"Things went her way, the draw opened up, Genie Bouchard hit her head and couldn't play that match [in round four]. It's just the way things happen sometimes."
Vinci will play fellow Italian Flavia Pennetta after she defeated Simona Halep in straight sets.
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