Only one of men's tennis' vaunted top four (Novak Djokovic) remains in Montreal, and only one top 10 seed (Victoria Azarenka) remains in Toronto.
Here's a look at how the damage was done to those six Slam champions Thursday:
Jo-Wilfried Tsonga (France) def. Roger Federer (Switzerland) 7-6(3), 4-6, 6-1 -- Failing to get revenge for his shocking five-set loss at Wimbledon, Roger Federer was again blown off the court in the deciding stages of a match against Jo-Wilfried Tsonga. Tsonga played exceptionally strong tennis in the third, reeling off five straight games to start the set before Federer finally was able to prevent the bagel in the sixth game.
Galina Voskoboeva (Kazakhstan)[Q] def. Maria Sharapova (Russia) 6-3, 7-5 -- Galina Voskoboeva's stunning run from qualifying to quarterfinals became even more impressive Thursday, knocking off Maria Sharapova in straight sets for her second top 10 victory of the week (and her career). Voskoboeva next faces Victoria Azarenka, a player she should certainly be able to contend with if she plays as well as she has the rest of this week. As if her week wasn't good enough, Voskoboeva is also into the quarterfinals in the doubles draw. That Alina Jidkova is some coach.
Samantha Stosur (Australia) def. Li Na (China) 6-2, 6-4 -- After seeing her pre-tournament interview with the WTA, I was pretty sure Li Na was not long for this tournament. Weeks relaxing and reveling in China seem to have dulled her game considerably, and Sam Stosur's weapons are simply too large to overcome when not sharp. Hopefully her focus and hunger comes back by the US Open.
Andrea Petkovic (Germany) def. Petra Kvitova (Czech Republic) 6-1, 6-2 -- Just like French Open champion Li Na, Wimbledon champion Petra Kvitova spent her time between Wimbledon and Canada reveling in her home country. Her rust was wildly apparent in this match, which Petkovic dominated from start to finish. Kvitova was never a model of consistency, so her inability to immediately back up her Wimbledon title shouldn't be too surprising. She'll win a lot of matches in her career, and a lot of tournaments, but it's hard to see her ever becoming a consistent workhorse No. 1 like a Justine Henin was.
Lucie Safarova (Czech Republic) def. Francesca Schiavone (Italy) 6-3, 6-3 -- Schiavone looked lethargic and uncharacteristically disinterested in the match, and Safarova took advantage. Safarova jumped ahead early in rallies, not giving Schiavone the time to build counterpunching rallies. The Czech lefty gets Serena Williams in the next round, a match she shouldn't figure to come close to winning.
Roberta Vinci (Italy) def. Ana Ivanovic (Serbia) 7-6(3), 6-2 -- While hardly a big upset in the rankings, still a disappointing loss for Ana Ivanovic, who should be a heavy favorite against a player like Vinci on hard courts. Vinci is having a career week, though, with this run to the quarterfinals and her first ever top five scalp against Caroline Wozniacki on Tuesday. Vinci will enter the top 20 for the first time in her career next week.
Stay tuned to SB Nation's coverage of the 2011 US Open Series at SBNation.com as well as on Twitter, @DailyForehand .