Toronto: Rafael Nadal recovered from a slow start, overcoming Marin Cilic 2-6, 6-4, 6-4 as the Spaniard's chase for a long-sought ATP Masters title on hardcourt heated up.
The world number one reached the semi-finals in Toronto and will next face Russian Karen Khachanov, who beat Robin Haase 6-3, 6-1.
Nadal last won a title at this level on cement in 2013.
"It was a very important match for me," Nadal said.
"Being in semi-finals is great news at the start of the hard court season.
"And winning three good matches in the first Master 1000, it's so important for me.
"He played unstoppable in the first set. I resisted, I played with the right tactic. I tried to find my solutions - but it was so difficult."
Stefanos Tsitsipas saved two match points to beat defending champion Alexander Zverev in their quarter-final contest 3-6, 7-6 (13/11), 6-4.
The Greek teenager, who turns 20 on Sunday's final day, defeated his third straight top 10 opponent at the tournament after knocking out Dominic Thiem in the second round and 13-time major winner Novak Djokovic in the third.
Tsitsipas is the youngest player to post three top 10 wins at a single tournament since the 19-year-old Nadal at Monte Carlo in 2006. Tsitsipas will next face Wimbledon runner-up Kevin Anderson, who beat Grigor Dimitrov 6-2, 6-2.
"I'm confused now, is this real?" 27th-ranked Tsitsipas said after completing his prestige hat-trick of upsets.
Nadal got caught on the back foot in the first set against Cilic, who took the opener on his fourth chance. Nadal struck
back in the second with a concluding break to square the match before taking victory with a break in the final game on his third match point after more than two hours.