Simona Halep overcame Ashleigh Barty in straight sets to set up a Western and Southern Open quarter-final against Lesia Tsurenko later on Friday.
World number one Halep triumphed 7-5 6-4 against Barty, who she beat en route to the Rogers Cup title last week, in one hour and 27 minutes to advance to the last eight in Cincinnati for the sixth time.
The Romanian will have to recover quickly before starting her match against Tsurenko on Stadium 3, providing the tournament is not hit by further rain delays that have blighted it this week.
"It was very tricky, she's a very tough opponent. The ball was really heavy but I'm really happy I got through this," said Halep in an on-court interview.
The French Open champion was on the back foot early in the first set when Barty broke her to love, but she hit straight back and the Australian's failure to return a cross-court backhand gave her a chance to serve out the set.
Barty fought back from 0-40 down to force deuce, but a long backhand slice from the baseline saw the match swing in Halep's favour.
The world number 16 again failed to consolidate a break of serve in the second and she paid the price as the Romanian raced to victory.