Wet weather hampered the proceedings at the WTA Tour Premier 5 event for a second straight day. She was in form during the tiebreaker, firing a service victor to convert her second set point under the warm sun at Aviva Centre.
All of the delays came in the first set and Wozniacki seemed to gain encouragement as she bounced back from 3-0 down.
Stephens, ranked 934th in the world, gave a good showing in her third tournament after missing 11 months due to a foot injury.
She became the first Ukrainian to reach the Top 10 in the WTA rankings by capturing the Dubai title in February where she beat Wozniacki.
After three rain delays and nearly three hours on court, Wozniacki eventually defeated world number one Karolina Pliskova 7-5 6-7 (3-7) 6-4. "Today was very hot, so I've been really struggling".
Stephens is making up for lost time on the court at the Rogers Cup, though, with her four matches this week taking almost eight hours in total. The finalist is to take home US$243,920. The obvious question with Svitolina is how much she has left in the tank after playing two matches on Saturday. So I tried just to have a better feeling in the end of the match but. "So I'm super happy with that". Pliskova faced a test in the round of sixteen as her opponent, Naomi Osaka, extended the World No. 1 to a third set. "She's strong there and she played her game". I have many tournaments ahead.
The 22-year-old Ukrainian received a bye into the second round, where she faced Daria Kasatkina of Russian Federation. "I'm just playing better". She'll face either Elina Svitolina or Simona Halep for the title. This is a quick turnaround that will really test the 22-year-old.