The winner of this match will face either Japanese wild card Misaki Doi or Russian Anastasia Pavlyuchenkova in the semifinals.
The win over Gibbs snapped a four-match losing streak for the three-time major champion, who hadn't won a match since Wimbledon and had not been past the second round of any event since Eastbourne.
The numbers say Kerber should win: as noted above, she's won eight of the previous ten matchups, is seeded higher and her counterpunching style plays perfectly against Keys' all-out aggression.
However, Keys is in better form, having won in Cincinnati and despite a disappointing performance against Elina Svitolina in the fourth round, has looked relatively sharp recently.
The American has struggled with her biggest weapon this week at times: her serve.
In the end, Kerber is far from her best and while she'll take plenty of confidence in her past success against Keys, she's not playing well enough to fall behind and recover.
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