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 realij" 27th-ranked Tsitsipas said after completing his prestige hat-trick of upsets.
Halep, Sloane enter semis
Montreal: World number one Simona Halep punched her ticket to the semi-finals of the WTA Canada tournament for the fourth straight year, cruising past France's Caroline Garcia 7-5, 6-1.
The 26-year-old Halep battled through a difficult first set, then easily won the second in a rematch of last year's quarter-final contest with Garcia which was also won by the Romanian.
"The first set was really tough," Halep said. "I just didn't give up at all in the first set. After I took it, I felt more confident.
"I felt that I'm moving better, I'm playing better, stronger. [Garcia] went a little bit down with energy after she lost that set."
While, US Open champion Sloane Stephens made the semi-finals for the second straight year, seeing off Anastasija Sevastova of latvia 6-2, 6-2.
Stephens will face defending champion Elina Svitolina, who eliminated Elise Mertens 7-5, 6-3.