Top-seeded Canadian Milos Raonic held off Juan Martin del Potro 6-3, 7-6 (8/6) on Saturday to book a title clash with Jack Sock at the ATP Delray Beach Open.
Despite some shaky moments, Raonic fought off a set point in the second-set tiebreaker and closed out the match with his 17th ace of the night to advance to the meeting with Sock, a 6-4, 7-6 (7/2) winner over fellow American Donald Young.
"You know it's going to be close, so it's about keeping disciplined and a positive attitude on the court," Raonic said.
World number four Raonic, forced out of the Davis Cup this month with a thigh injury he suffered during the Australian Open, broke del Potro in the 11th game of the second set to serve for the match.
But the big-serving 26-year-old was broken back, firing a forehand wide to give del Potro a break point which the 2009 US Open winner converted with a backhand winner.
Raonic was close again with a 5-4 lead in the tiebreaker and two service points to come. But he double-faulted and sent a forehand wide to give del Potro a set point that the seventh seed couldn't convert.
Another forehand long from del Potro gave Raonic a 7-6 lead and the Canadian won a third straight point to reach his first final of 2017.
"He was coming so fast to my game and slice that I couldn't manage my backhands," del Potro said. "I tried my best, but he was too good."
Sock will be seeking to add a second title of the year to the one he lifted in Auckland in January.
He saved the only break point he faced in the match and won the last seven points of the second-set tiebreaker to seize the victory.
Sock said his storming finish belied the challenge posed by Young.
"It definitely could have gone either way in the first set," Sock said. "He's a tricky player in that he makes you play a lot of balls and can wear you down, but also has great hands at the net when he comes forward.
"You never totally know what you're going to get, so I was just fortunate to come through in two sets."