Venus topped Serena 6-7 (2), 6-2, 6-3 on Saturday in the hard-court event for her first victory over her sister since 2009 in Dubai.
"I think for both of us, what's so unique about the situation is that we're both very good players," Venus said. "I think typically you may have some siblings, one is quite good, one is not as good so you kind of know what the result is. I think we both know when we walk out there, it's not like you're guaranteed a win. I think that's what makes it challenging for both of us."
The 32-year-old Serena, ranked No. 1 in the world for the 200th career week, leads the series 14-11 and had won the last five matches. The 34-year-old Venus, ranked 26th, ended her sister's 14-match Rogers Cup winning streak that dated to wins at the 2011 and 2013 tournaments in Toronto. Serena skipped the 2012 event in Montreal.
"I don't think I played a great game today," Serena said. "Let's just face it, I served well in the first set, but that was that. So, I definitely need to go back and analyze it, figure out how to be more consistent."
In the second semifinal, third-seeded Agnieszka Radwanska beat Ekaterina Makarova 7-6 (1), 7-6 (3).
"I definitely don't want to have a letdown and get out there and not play at least half as well," Venus said about the final. "I don't want to put any pressure on myself, but I want to go out there and perform just as well. It would mean a lot to me because I've been dreaming of winning a tournament at this level since I got back on tour. You try and you try. There are disappointments. One day you get a little closer. So this is my 'little closer' right now."
Venus won the last of her 45 titles in Dubai in February. She uses medication, a vegan diet and rest to control Sjogren's Syndrome, an auto-immune disease she was diagnosed with in 2011.
Unseeded Venus started the match strong on her serve and took a 3-1 lead, but Serena rallied to tie it at 3 and went on to take the set in a tiebreaker. Venus dominated the second set, breaking Serena's serve twice and taking advantage of unforced errors.
Serena made two errors and dropped serve to fall behind 4-2 in the third set. Venus, who dropped serve only once in the match, served for the win at 5-3. Venus hit a rocket serve on her third match point that Serena returned into the net. Serena had 19 aces and nine double faults, and Venus had six aces and two doubles faults.
Serena was coming off a victory last week in Stanford, California, in her first tournament since withdrawing from a doubles match at Wimbledon because of equilibrium problems.
Serena, who has 17 Grand Slam titles, has struggled in the majors this year. She was beaten in the fourth round at the Australian Open, second round at the French Open and third round at Wimbledon.
"I haven't even been able to get to the quarterfinals of a Grand Slam this year," Serena said. "At this point, I'm really just looking forward to next year, to be honest."
She was quick to point out that didn't mean she's giving up on the US Open, where she is the two-time defending champion.
"I'm just saying I've had a really disappointing year, for me, especially in the Grand Slams," she said. "So I'm not going to put any pressure on myself.
"I almost feel like the pressure is lifted because I haven't performed the way I've wanted to. In a way, I don't feel a ton of pressure going into the Open. I almost feel like it's lifted. I look forward to next year because I don't have any points to defend at any of the slams."
Venus Defeats Serena In Montreal
Venus Williams knocked off sister Serena in three sets to advance to the final of the Rogers Cup in Montreal.
Venus Williams Reaches Final In Montreal
Venus Williams reacts to defeating her sister Serena to make the final in Montreal.