McEnroe, a 1989 Roland Garros doubles victor and 1991 Australian Open singles semifinalist, said that Del Potro complained a lot during the Indian Wells about the crowd cheering after his first serve faults against Roger Federer, who counted on a big support from spectators.
This will be Isner's fourth Masters 1000 final, and playing the way he's ousted del Potro, sensation Hyeon Chung, and Marin Cilic, he will be hungry for the biggest win of his career.
The Argentine most recently defeated Canada's Milos Raonic in the Miami Open quarterfinals on Wednesday night and will face American John Isner in the semifinals Friday.
The first set, in which Isner fired down 19 winners, was sealed in typical fashion with a brutal serve out wide, but the second proved far more attritional. He never faced a break point all match, and in the tie-break, his volleys were the difference.
It was the first semi-final match of the day, with the American dominating proceedings and del Potro, playing out-of-sort. "He was too good for me".
"I was fortunate to get a del Potro who is very, very low on fuel", Isner said. "I'm toward the latter part of my career; this is the best moment of my career".
"I've just continued to keep playing better", Isner said.
"I'm happy where I am right now, and hopefully it will be another great match here and then I can go to the clay court season", he said.
"I love to play in matches like this", a visibly tired del Potro said after his 15th straight match win.
Unlike Isner, Zverev was challenged in the opening set and needed a tightly contested tiebreak to seize early momentum. "I'm going to be very tough to beat.", he said.
While the victor didn't have the sheer number of aces Isner did in the first match with 10, he controlled the match with his serve and won 88 percent of his first-service points, per the ATP World Tour website. "Not many players can return his serves".
The 14 seeded Isner will play No. 4 seed Alexander Zverev in the final on Sunday.
Even so, Isner knew he was the fresher player. The 20-year-old German bested No. 16 Pablo Carreno Busta of Spain 7-6 (4), 6-2.
Isner saw another five chances to break come and go in tense decider before his persistence paid off when Zverev thudded a backhand into the net, prompting him to demolish his racket in a fit of rage.