Madison Keys stunned top seed Iga Swiatek 6-3 6-4 to book her place in the quarter-finals of the Western & Southern Open on Thursday.
Keys arrived in the contest seeking a first career victory over a reigning world number one in six attempts, having failed to win a set in each of the previous five.
The 2019 champion had also lost her previous two showdowns with Swiatek, including a resounding 6-1 6-0 defeat in the Indian Wells Open quarter-finals earlier this year.
After the first games went with serve, Keys went into overdrive; reeling off nine successive games to take full command of the contest at 6-3 5-0.
Swiatek rallied as she rescued match point to avoid the bagel, winning 11 of 12 points to reduce the second-set deficit to 5-3.
The winner of six WTA titles this season, the Pole saved a further match point in the ninth game before claiming what appeared to be another crucial break of serve.
However, former US Open finalist Keys responded magnificently to make it third time lucky against Swiatek, who is now 4-4 since her 37-match winning streak ended with defeat by Alize Cornet at Wimbledon.