Williams, who won the title last year in Toronto, is back in Montreal for the first time in 14 years, while Venus is making her first ever visit to the belle province, but it could be a memorable one.
If Venus can see off 14th seeded Spaniard Carla Suarez Navarro later on Friday it would setup the 25th meeting between the sisters and first since a 2013 semi-final clash in Charleston won by Serena.
Both Serena Williams and Wozniacki arrived in Montreal in winning form.
Williams, a three-time champion on the Canadian hard courts, picked up her 61st career title last week at Stanford while Wozniacki was champion in Istanbul. Neither had dropped a set on route to the quarter-finals.
The match served up plenty of intrigue, Williams, the defending champion and current world number one, going against a former-number one and former-champion, who has her own love affair with the Montreal hard courts where she had built a 9-1 record.
The muscular American was certainly not going to outwork Wozniacki, who is training to run the New York City marathon in November, but Williams had enough weapons and experience to see off the dangerous Dane.
In the opening set Wozniacki had one break point and made it count while Williams could not convert either of her two opportunities.
Wozniacki again took the initiative in the second, breaking the 17-time grand slam winner at the first opportunity but Williams would not throw in the towel, sweeping three straight games to surge in front 5-4 and then break the Dane to close out the set.
After trading a pair of breaks to start the third it was Williams delivering the knockout punch, with one last break to clinch the match.
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