Wozniacki advanced to the semifinals of the US$2.17-million hardcourt tournament with a 6-4, 6-4 victory over Canada's top female player despite the wildly pro-Wozniak crowd at Uniprix Stadium on Saturday night.
The two players with similar names have met nine times, and Wozniak's only win was in Tokyo in 2009 when the Dane was forced to retire with a viral infection in the first set.
''It feels like she always comes up with her best tennis against me, for some reason,'' said Wozniak. ''Every time I see we're playing each other I want to step it up also.
''Hopefully next time it's my win.''
Earlier in the day, Wozniak, of Blainville, Que., finished off a rain-delayed match by topping American Christina McHale 7-6 (5), 6-3. That made her the first Canadian in 20 years to reach the quarter-finals of the event some still call the Canadian Open.
Wozniak and Wozniacki are both of Polish descent, but one was born in Canada and the other in Denmark.
Wozniacki, the seventh seed who won in Montreal in 2010, is to face fifth-seeded Petra Kvitova in the semifinals on Sunday. Kvitova ousted Tamira Paszek 6-3, 6-2.
Veteran Na Li, the 10th seed, will meet 16th-seeded Lucie Safarova in the other semi. Safarova downed unseeded Roberta Vinci 6-2, 6-2. Li has won her last five meetings with Safarova.
The final is scheduled for Monday night.
Wozniacki was playing her second full match of the day.
In the afternoon, she reached the quarters by beating American Varvara Lepchenko 4-6, 6-3, 6-4. She received treatment at courtside for a right leg problem early in the second set but was able to complete the match and later did not look bothered by it against Wozniak.
''I started feeling things in my knee,'' she said. ''I put the tape on it and it felt much better. I didn't feel it at all out there.''
Li finished up a rain-delayed third-round match with a 6-4, 6-2 win over eighth-seeded Sara Errani early Saturday, then ousted No. 2 seed Agnieszka Radwanska 6-2, 6-1 in only 70 minutes.
Rain continued to plague the tournament, with the start of evening matches delayed 90 minutes by a heavy downpour. But the day's entire schedule was played.
Wozniak was one game from defeating McHale on Friday night when their third-round match was halted by rain. She needed only a few minutes to close out the match.
She became the first Canadian since Patricia Hy-Boulais in 1992 to reach the quarter-finals. Helen Kelesi in 1987 and Carling Bassett in 1985 were other Canadians to get that far.
She earned US$41,450, and the 225 points should put her into the world's top 50. Wozniak said that after two years of injuries, she's starting to feel like she did at her peak in 2009 when she got to 21st.
''It's a beautiful week I had here,'' she said. ''It means so much to me, coming here since I was a little girl with my parents to watch the best.
''I wish I could come back (Sunday), but I played a great player. I went after my shots. I did everything I could. My offensive game is coming back and I'm gaining confidence, so it's encouraging.''
Radwanska also had to complete a match that started on Friday and posted a 6-2, 6-4 win over Chanelle Scheepers. She had little left for Li in the quarter-final.
''It's a little bit too much, two singles in one day,'' said Radwanska. ''I think the first match cost me a lot of power.
''It was very hot conditions out there. Two hours later I was playing my second match. Of course she had the same situation. She was just playing too good. I really couldn't do anything.''
When both top-ranked Victoria Azaraneko and No. 2 Maria Sharapova pulled out with injuries, Radwanska was in position to take over the world No. 1 ranking if she won the tournament. That chance slipped away with the defeat.
''I just hope I have more opportunities to be No. 1,'' said Radwanska, who will play next week in Cincinnati. ''Of course I'm going to fight for that every week."
Li said she was glad to get her matches done before the rain.
''I played unbelievable for both matches,'' she said. ''It was the first match I played against Errani, as well.
''I don't know what happened. I had a day off yesterday. I was ready to play, but finally they cancelled, so I was a little bit worried.''
In other early action, Radwanska downed Chanelle Scheepers 6-2, 6-4 and Vinci downed No. 6 Angelique Kerber 6-2, 7-6 (7), while Paszek beat Carla Suarez Navarro 6-3, 6-0.