Fifth-seeded Italian Flavio Cobolli out-lasted Miomir Kecmanovic 7-6 (7/5), 3-6, 6-4 on Friday to book a title clash with Frances Tiafoe in the ATP hardcourt tournament in Acapulco.
Cobolli trailed 1-3 in the final set but won five of the next six games to stay on course for a third ATP title to go with claycourt victories in Bucharest and Hamburg last year.
The 23-year-old from Florence fended off two break points at 3-3 in the third, saving both with forehand winners.
Unble to serve out the match at 5-3 he broke Kecmanovic in the next game to secure the victory over the Serbian – who had beaten world No 4 Alexander Zverev in the second round.
"I think we both played an amazing match," Cobolli said. "I was a little bit lucky at the end, because at the crucial points sometimes you need luck. I'm really proud of myself because it wasn't easy to come back."
Eighth-seeded Tiafoe rallied from a set and a break down to beat fellow American Brandon Nakashima 3-6, 7-6 (8/6), 6-4.