Madrid - Victoria Azarenka has double-faulted on match point and allowed Serena Williams to reach the Madrid Open quarter-finals with a 7-6 (5), 3-6, 7-6 (1) win on Wednesday.
After early breaks in the deciding set, Williams overshot a forehand to trail 6-5.
Azarenka reached match point on serve, but double-faulted.
Three consecutive double faults made it 6-6.
Williams dominated the tiebreaker, and improved her head-to-head record against Azarenka to 9-0.
After an injury-affected season last year, Azarenka, a two-time finalist, was unseeded in Madrid for the first time.