The 19-year-old took the first set in 29 minutes but suffered an injury to her left thigh in the second, which affected her movement and allowed her American compatriot to seize a 4-1 lead following a double break.
Keys took a medical timeout after that game and returned with strapping around her leg and somehow broke Williams twice to get it back on serve, but was then broken again and Williams served out the set 6-4.
In the decider, Williams earned a double break and was serving to take a 5-3 lead but Keys broke for the second time to level it at 4-4.
The emerging American talent then broke again in the final game to clinch the match and set up a semi-final against either Venus' sister Serena or last year's beaten finalist, Dominika Cibulkova.
(Reporting by Greg Stutchbury; Editing by Peter Rutherford)
Share
