John Isner produced a blistering Miami Open semi-final display against crowd favourite Juan Martin del Potro to win 6-1, 7-6 (7/2) and snap the former US Open champion's 15-match winning streak. It was a phenomenal effort from the American who blasted down 13 aces and took just one hour and 23 minutes to floor Argentina's Del Potro and book his place in Sunday's final. Isner will meet world number five Alexander Zverev in the final after the German rolled over Spaniard Pablo Carreno Busta 7-6 (7/4), 6-2 in the other semi-final.
"I have played a lot of big matches and not been able to get such a good start but I am playing some of the best tennis I have played in such a long time," Isner said.
"I started the tournament well and I have improved with every game. I am super fresh and ready to go for the final."
An exhausted Del Potro said he is looking forward to some much-needed time away from tennis before deciding on when to play next.
Winning the Miami Open final would have seen him climb to world number three but simply staying fit for the French Open in May is the ultimate goal.
French Open target
"I don't want to think about tennis right now," said the Argentine.
"I just want to stay healthy and maybe I will miss a few tournaments to get ready for the French Open. We will come up with a schedule for the clay court season.
"I will go home now, eat some barbeque, spend time with friends and not talk about tennis for the next few weeks."
Isner, who won an impressive 83 percent of points on his second serve, was aiming to reach his fifth ATP Masters final and, finally, emerge victorious from one after four defeats.
The American had never reached the showpiece here but knew that with the fit again Del Potro in such devastating form and unbeaten in his last 15 matches, it would take a monumental effort to upset the Argentine and his hordes of followers at Crandon Park.
The American wasted no time in breaking Del Potro and racing into a 3-0 lead while sending down five aces on his own serve to brilliantly wrap up the first set in just 27 minutes.
The second set was a tight affair, going into the ninth game with the match delicately poised at 4-4.
Isner suddenly had a chance to break which was saved by Del Potro after the world number 17 hit the net, a mistake which was punished by an ace and drop shot from the crowd favourite.
Deafening chants of 'Delpo, Delpo' rang around the main stadium here as the 29-year-old tried to force a deciding set yet Isner's serve held firm to force a tie-break.
The momentum was with the American, his serve reaching 136 mph as he flew into a 3-0 lead.
Isner's serve was relentless and on target every single time making it impossible for Del Potro to get a foothold in the game, and when an excellent passing shot gave Isner four match points, he took the first with a brilliant drop volley to complete one of the finest wins of his career.
"When he plays like that, he's one of the toughest guys on tour to beat," Del Potro said.
Fourth seeded Zverev needed 88 minutes to oust Carreno Busta and punch his ticket to the final.
The 20-year-old Zverev will be seeking his seventh career ATP title and first of the season when he faces Isner.
Zverev blasted 10 aces and won 88 percent of his first serve points in his first career meeting with the 26-year-old Carreno Busta.
"Every day I want to serve big," said Zverev, who improved to 13-4 on the season. "I was very fortunate to win the first set and then I found my game in the second set."