Williams lost only 12 points while winning the first nine games and will face Ana Ivanovic, who beat Sloane Stephens 2-6, 6-4, 6-1.
With 68 per cent of his first service in, Novak Djokovic got his first breakthrough when he broke Wawrinka in the ninth game to take 5-4 lead and his service to follow.
The remaining quarter-final matches are Richard Gasquet (France) – Andy Murray (UK) and Feliciano Lopez (Spain) – Roger Federer (Switzerland).
Djokovic will next play fifth-seed Stan Wawrinka.
The 12th-ranked Swiss teenager who beat Serena Williams and Simona Halep on her way to the Toronto trophy last weekend, lasted only 33 minutes, receiving treatment midway through the set on her right wrist. I did that very well tonight, so I am really pleased it was a rock solid performance. Federer, the defending champion, is trying for an unprecedented seventh title.
Two-time Australian Open champion Victoria Azarenka had to stop with leg pain after being taped at the end of the first set, handing a 1-6, 3-0 win to Russian Anastasia Pavlyuchenkova.
“I’m exhausted, my body hurts”.
Afterwards, Murray told Sky Sports 3: “I think I was striking the ball well, better as match went on”.
Djokovic lost the first set to the world number 66 – as he had in Miami earlier this year – but battled back to claim a 4-6 7-6 (7/5) 6-2 victory.
“I’m excited to be in another final”, said Federer, who has beaten Djokovic in two Cincinnati finals. Afterwards, Wawrinka said he’s received a lot of support from players, following the rude comments Nick Kyrgios made about his girlfriend last week. Both men were coming off of three-setters in their previous rounds as Djokovic came back from double break down in the third to defeat David Goffin. She beat 14th-seeded Elina Svitolina 6-4, 6-3. “If you seldom get broken or you don’t get broken in a match, it’s quite hard to lose at this point”. “I’m excited for US Open“.
A victory Sunday would make him the first player to win all nine ATP Masters during his career. “I know where I am. This guy, even when he’s not playing his best, he can beat me the way he did today”.
Top seed Novak Djokovic and Stan Wawrinka each survived a scare at the Western & Southern Open on Thursday to reach the quarter-finals where they will clash in a rematch of the French Open final.
He also continued to feel good physically a week after he received on-court treatment for an elbow ailment at the Rogers Cup in Montreal.