Angelique Kerber and Venus Williams progressed at the Rogers Cup on Wednesday in what was a mixed day for seeds.
Kerber, runner-up at Wimbledon earlier this month, battled past Mirjana Lucic-Baroni, while Venus eased through Barbora Strycova in Montreal.
Johanna Konta, winner of the Bank of the West Classic last week, defeated Vania King, and Agnieszka Radwanska moved past Monica Niculescu at the WTA Premier event.
However, Sam Stosur went down to Daria Kasatkina, Carla Suarez Navarro suffered a shock loss against Kristina Kucova, and Dominika Cibulkova lost out to Eugenie Bouchard.
KERBER, VENUS PROGRESS
Second seed Kerber was taken to a third set by Lucic-Baroni, but prevailed 6-3 4-6 6-3 in the day's late match.
Meanwhile, Venus had a far easier time against Strycova, advancing 6-3 6-0 in a match that lasted just under an hour.
MIXED DAY FOR SEEDS
Every seed in action progressed on both Monday and Tuesday, but Wednesday provided some upsets.
Along with Konta and Radwanska, 10th seed Madison Keys advanced after beating fellow American Madison Brengle 6-4 6-3, and the ninth-seeded Svetlana Kuznetsova beat Alla Kudryavtseva 7-5 6-0 in an all-Russian affair.
The seventh-seeded Roberta Vinci beat Italian counterpart Camila Giorgi 2-6 6-3 6-4, Karolina Pliskova had a walkover against Sara Errani, Anastasia Pavlyuchenkova defeated Christina McHale 6-2 7-5, and Petra Kvitova knocked out Andrea Petkovic in a 6-2 6-4 win.
But Kasatkina knocked out 13th seed Stosur 7-6 (7-1) 6-3, the eight-seeded Suarez Navarro was eliminated by Kucova, who came from behind to win 3-6 6-4 6-4, and Bouchard breezed past Cibulkova 6-2 6-0.
VENUS FEELING GOOD
The 36-year-old advanced to the third round with a comfortable win against Strycova, much to her surprise.
"It was definitely more straightforward I think than all of our other matches," Williams said after the match. "I didn't mind that, especially after playing a lot last week, just to be able to come out and hopefully advance to the next round.
"It's been intense. Usually I don't play this much back-to-back. But I knew what I was going to do going into the year, what it was going to take. I never sign up for anything that I don't think I can achieve."
HALEP, VENUS IN ACTION
Simona Halep will be looking to make the quarter-finals when she faces Karolina Pliskova, while Venus tackles Keys in an all-American encounter.