Top-seeded Stefanos Tsitsipas clawed his way past Felix Auger-Aliassime 7-5, 4-6, 6-3 on Thursday to reach the semi-finals of the ATP hardcourt tournament in Acapulco.
The world number five from Greece will take on Italian qualifier Lorenzo Musetti, who defeated fifth-seeded Bulgarian Grigor Dimitrov 6-4, 7-6 (7/3).
Tsitsipas dropped his opening service game against the seventh-seeded Canadian, clawing back with a break before finally reeling off the last six points of the opening set.
He couldn't maintain the momentum, however, going down an early break again in the second set as Auger-Aliassime leveled the match.
The third set was a tense affair and it was Auger-Aliassime who cracked, coughing up back-to-back double faults to hand Tsitsipas the first break of the frame for a 5-3 lead and a chance to serve out the match.
Tsitsipas, who is vying to reach a first final of 2021, reached the semi-finals at the Australian Open in February and at Rotterdam earlier this month, but is coming off a quarter-final ouster by 93rd-ranked Pierre-Hugues Herbert in Marseille.
Musetti, 19 and ranked 120th in the world, is through to his second career semi-final in his fourth ATP Tour main draw appearance.
Dimitrov, the 2014 Acapulco champion, made the teenager work for his final four berth, saving six match points before finally pushing a forehand wide on Musetti's seventh opportunity.
The other semi-final will be an all-German affair between second-seeded Alexander Zverev and Dominik Koepfer.
Zverev, runner-up to Australian Nick Kyrgios in Acapulco in 2019, advanced by walkover when Norway's Casper Ruud withdrew from their scheduled quarter-final with a right wrist injury.
Koepfer, ranked 71st in the world, booked his first tour-level semi-final with a 7-5, 6-4 victory over Britain's Cameron Norrie.
Like Musetti, Koepfer needed multiple match points to seal his win.
"I had four match points on his serve, but I couldn't get it done," he said. "I got a bit tight, I'm not going to lie. I was nervous and I knew I would have to make a lot of first serves.
"It was a huge relief after such a good week so far," he added. "I'm really excited to play again tomorrow."