The win saw the former world number three earn his first ATP Masters 1000 quarter-final since November 2015.
The fourth-seeded Spaniard saved three match points in the deciding set with Keys serving at 6-5, and 40-15.
Rafael Nadal says he knows more than anyone else what it's like to be injured and miss big tournaments.
Victoria Azarenka has announced she is likely to miss the US Open at Flushing Meadows because she is not able to travel with her son.
Rising star Alexander Zverev took time to reflect on his season so far after his exit from the Cincinnati Masters on Wednesday.
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