Kuznetsova had beaten Bouchard in their only previous meeting, on the clay courts of Oeiras earlier this year, and she took it to her again on the hardcourts of Cincinnati, coming out strong with a set and a break lead, 6-4, 1-0. Bouchard rallied to take the second set but from 2-all in the third it was all Kuznetsova again, who reeled off four straight games to close the match out, 6-4, 3-6, 6-2.
Kuznetsova had fewer winners than Bouchard in the match, 23 to 28, but far fewer unforced errors, 28 to 46. And at the end of the day the former World No.2 scored the 45th Top 10 win of her career.
"It was a little bit up and down but I think we both played great," Kuznetsova said. "Genie really raised her level in the second and third sets, but I was defending really well, and it was just a really exciting match for me to play out there. It was a great atmosphere. Thanks to everybody for coming out."
The biggest surprise of the day saw No.3 seed Petra Kvitova fall to Elina Svitolina, 6-2, 7-6(2), breaking back twice when the WTA Rising Star served for the match but eventually falling in the tie-break.
"From the beginning I didn't feel very comfortable out there," Kvitova said. "I was really trying to fight, but I just wasn't able to do it today. I'm not sure why. But it happened. I'm just glad I entered New Haven next week, so I still have a chance for more matches under my belt before the US Open."
Kvitova was then asked if she was at least hitting well in practice. "Not really," she replied.
Svitolina's win over the World No.4 was the first Top 10 win of her blossoming career.
There was another upset as Sabine Lisicki outlasted No.14 seed Sara Errani, 6-4, 2-6, 7-6(2), twice rallying from a break down in the third set to win in a few minutes shy of three hours. Lisicki hit 18 double faults - but she finished on a high, hitting her sixth ace of the match on match point.
Earlier in the day, No.1 seed Serena Williams made a winning start in her quest for a first Western & Southern Open title, though it wasn't easy by any means - 24 service games, no breaks, and two set points for Sam Stosur in the second set tie-break before Williams squeaked through, 7-6(7), 7-6(7).
"It was just a great match," Williams said. "She served unbelievable, and I was like, 'I can't lose serve because she's just serving great.' She has one of the best second serves on the tour, for sure. She has a kick serve that just bounces so high. And she can fool you because she can also swing it up the T or go into the body. And most ladies don't hit their second serve at 98 or 102 miles an hour.
"This is why she was able to win a Grand Slam, because she played like that today."
Elsewhere, No.4 seed Agnieszka Radwanska beat Kurumi Nara, 6-2, 6-2, No.6 seed Angelique Kerber beat Ekaterina Makarova, 6-4, 6-1, No.8 seed Jelena Jankovic held off German qualifier Annika Beck, 6-1, 7-6(0), and No.9 seed Ana Ivanovic defeated American qualifier Christina McHale, 6-4, 6-0.