Toronto - Rafael Nadal beat Karen Khachanov 7-6 (7/3), 6-4 on Saturday to set up a final with birthday boy Stefano Tsitsipas at the Toronto Masters.
The Spanish icon will try on Sunday to spoil the 20th celebrations of the Greek youngster who reached the second final of his career by beating Wimbledon finalist Kevin Anderson 6-7 (4/7), 6-4, 7-6 (9/7), saving a match point in victory.
World number one Nadal won a battle of the tennis generations with Tsitsipas last April in the Barcelona title match.
"To win this match is important, it's very important to be in the final of Toronto," Nadal said after running his season record to 39-3 in a match which ended after midnight local time.
"I'm motivated every day when I wake up, there is always something to improve," said the 32-year-old.
"I want to stay around for as long as possible (in tennis)."
Top seed Nadal edged out the first set in a tiebreaker after a two-hour, rain-delayed start.
In the second, Nadal went about finishing up his business with a break in the third game and on his way to the win in just over an hour and a quarter.
Nadal leads the all-time list of Masters 1000 titles on 32.
He will be playing his 116th ATP final and stands two wins away from 80 trophies.
Tsitsipas, who will move to at least 15th in the rankings, became the first man since Jo-Wilfried Tsonga here in 2014 to defeat four Top 10 players at the same event.
He dispatched Dominic Thiem, Novak Djokovic, and Alexander Zverev before downing Anderson.
He will be the first unseeded finalist in Canada since Nicolas Kiefer in 2008.
"It feels like I'm playing Davis Cup and everyone is backing me up and they're so supportive," Tsitsipas said.
"Four wins against top 10 players. I would never imagine that I could pull this out in a single tournament.
"I don't know if I got lucky with all those players, but somehow it happened that I played four top 10 and managed to beat them, which is a huge achievement for me and for my game this week."
Tsitsipas worked for two hours, 48 minutes to secure his upset of the hard-serving South African, with Anderson going down with 10 aces.
"It doesn't matter what the score. I'm always going to attack. I'm always going to go to the ball," Tsitsipas said.
"My forehand is on fire at this moment. Hopefully it can remain like this tomorrow because it will be super important for me, the win tomorrow."
The outcome over Anderson was decided in a tight third-set tiebreaker, with Tsitsipas blowing his first two winning chances with a double-fault and a forehand error.
Anderson missed out on a match point off his own serve as Tsitsipas slammed over a backhand cross-court winner.
The Greek saved all four break points he faced while breaking Anderson once in the afternoon struggle.
"It's obviously incredibly difficult losing a match like where it's so close at such a big stage of the tournament," Anderson said.
"I did what I could. I thought he played some really good tennis, especially when it mattered the most.
"On the one match point that I had, he came up with an unbelievable backhand cross-court winner - it was a very impressive effort from him."
Results from the ATP Toronto Masters tournament on Saturday (x denotes seeding):
Rafael Nadal (ESP x1) bt Karen Khachanov (RUS) 7-6 (7/3), 6-4
Stefanos Tsitsipas (GRE) bt Kevin Anderson (RSA x4) 6-7 (4/7), 6-4, 7-6 (9/7)