Big-hitting American John Isner kept his title defence alive but needed all his experience to see off Canadian teenager Felix Auger-Aliassime 7-6(3), 7-6(4) on Friday to return to the Miami Open final.
The 18-year-old Canadian led Isner 5-3 in each set and both times allowed the defending champion off the hook, unable to deliver the knockout, as the towering American fought back and extended his tiebreak record to 9-0 in the tournament.
Isner will meet Roger Federer, who cruised into his fifth Miami Open final with an impressive 6-2, 6-4 victory over Canadian teenager Denis Shapovalov later on Friday.
"For sure (it was) nerves," said Auger-Aliassime, the youngest men's semi-finalist in the tournament's 35-year history. "It's like I caught a virus or something. I don't know. I couldn't put a second serve anymore.
"Even the first serve, if you put it in, you don't have to hit the second serve. That's just very tough to swallow."
Auger-Aliassime had appeared unbothered by being on the big stage against the crowd favourite playing attacking, aggressive tennis that rewarded him with the early break in each set.
Yet serving for the set, the 18-year-old's inexperience and nerves were exposed.
While Isner conceded his experience was a plus, he said it was not the deciding factor.
"I think it (experience) may have helped a little bit," said Isner. "But you see a lot of times where someone can have all the experience in the world or some teams can have all the experience in the world and they don't come through against an inexperienced opponent.
"Maybe he was a little bit fatigued because he came through qualifying.
"So could have been a little bit of inexperience and maybe a little bit of fatigue, also."
Serving for the first set, the Canadian produced three of his seven double faults, opening the door for the 33-year-old American who went on to take the first tiebreak 7-3.
Auger-Aliassime regrouped and was on the attack again in the second, grabbing the early break to nose in front 4-2.
Again serving for the set at 5-3, he let Isner back in the contest as the American got back on serve with the help of yet another Auger-Aliassime double fault.
While Auger-Aliassime was misfiring, Isner's serve was booming, as he blasted 21 aces past his opponent.
"I just felt like, I don't know, the nerves got to me a little," said Auger-Aliassime. "I wasn't able to do like all the other matches and just focus on what I had to do, and it really got to me too hard."
Federer was dominant in service and broke the 19-year-old three times.
The Swiss ace took control of his semi-final early, breaking Shapovalov in the third game as his young opponent shanked a backhand.
Federer broke again in the third game of the second set and served his way into the final against defending champion Isner, who is yet to drop a set in the tournament this year.