Karolina Pliskova is through to the last eight at the Rogers Cup after third-round opponent Naomi Osaka was forced to retire in the final set.
World number one Pliskova, who topped the WTA rankings for the first time last month, was leading 6-2 6-7 (4/7) 1-0 in Toronto when Japan's Osaka withdrew due to an abdominal injury after losing the opening game in the decider.
Teenager Osaka said she first felt the injury during qualifying, but was still able to trouble Pliskova before pulling out and the world number 50 extended the match by taking the second-set tie-break.
But Pliskova, who faces a battle with Romania's Simone Halep in a bid to retain her number-one spot, will be pleased with her display after firing down 12 aces and saving all three of the break points she faced.
Pliskova will next meet Caroline Wozniacki after the Danish world number six beat Poland's Agnieszka Radwanska 6-3 6-1.
Defending champion and second seed Halep raced through to the last eight, losing just one game in a one-sided 6-0 6-1 victory against Czech Barbora Strycova.
Halep will now play France's Caroline Garcia, who ended the run of Catherine Bellis, beating the American 6-4 6-2, while Czech Lucie Safrova overcame Johanna Konta's second-round conqueror Ekaterina Makarova of Russia 6-3 6-7 (3/7) 6-2.