Several players were forced to play two matches in the day, with rain having severely affected the schedule at the Canadian hardcourt event, but Li made light of the heavy workload as she cruised to two straight-sets victories.
The 10th seed first overcame eighth-seeded Italian Sara Errani 6-4 6-2 in the delayed third-round clash and then saw off Poland’s world number three Radwanska even more convincingly to advance to a last-four match-up with Lucie Safarova.
The 16th-seeded Czech, who on Friday knocked out US Open champion Samantha Stosur, continued her fine form with a comfortable 6-2 6-2 triumph over Italy’s Roberta Vinci.
Vinci earlier ousted sixth-seeded German Angelique Kerber 6-2 7-6 (9/7). The second semi-final will pit 2011 Wimbledon champion Petra Kvitova against former world number one Caroline Wozniacki.
Fifth-seeded Czech Kvitova advanced by breezing past Austria’s Tamira Paszek 6-3 6-2 in their last-eight encounter.