Miami, USA: Defending champion John Isner ended Canadian teen Felix Auger-Aliassime's dream run on Friday and advanced to the ATP Miami Open final with a 7-6 (7/3), 7-6 (7/4) triumph.
Backed by his huge serve, the 33 year-old American fired his 21st ace to complete the victory after one hour and 53 minutes to book a spot in Sunday's final against the winner of a later match between Swiss star Roger Federer and Canada's Denis Shapovalov.
"It's amazing to be back in the final," said Isner, who hit 32 winners compared to 20 by Auger-Aliassime. "I am so happy to be one match away from defending the title."
The youngster from Montreal competed confidently in the biggest match of his career but will rue the chances that escaped him after being broken while serving for the first and second set.
"To break while Felix was serving for both sets was unusual but I have felt comfortable all tournament and feel I am playing well," Isner said.
There was a huge buzz surrounding the 18-year-old Canadian in the lead up to his first ever ATP Masters semi-final, a spotlight brightening through his brilliant run from qualifying to the last four.
Auger-Aliassime is the youngest-ever male semi-finalist in Miami and only the second qualifier to reach the last four after Guillermo Canas reached the same stage in 2007 before losing to Novak Djokovic in the final.
Despite his defeat, Auger-Aliassime will see his ranking jump from 55 to 33 in the world next week.
"I did the best I could," Auger-Aliassime said. "But they are chances you can't miss. It was nerves. I couldn't get a second serve in. It's tough to take."
Isner, 15 years older and six inches (15.24 cm) taller than his rival, had only been broken twice in 48 service games at Miami and it wasn't long before the youngster realized what makes his booming serve so difficult to break down.
A golden opportunity arose at 2-3 only for Isner to save three break points, but Auger-Aliassime regrouped and managed to finally lead 4-3.
But the Canadian double faulted while attempting to serve for the set and in the tie-breaker, the world number nine kept the pressure on.
Auger-Aliassime was unable to hold at 4-3 and that gave Isner the platform to seal the first set.
In the second set, a brilliant backhand winner set up another break chance and when Isner hit long, the Canadian moved 4-2 ahead and superbly held with an ace to extend his advantage.
But serving to level the match, the Canadian surrendered his third double fault and when Auger-Aliassime netted an straightforward volley, the match was back on serve and destined for another tie-breaker.
A final ace extended Isner's unblemished tie-breaker record for the event and ended Auger-Aliassime's career record against top-20 opponents, which was 5-0 entering the match.