However, a dominant performance from Isner put paid to those hopes, as the powerful American claimed a 6-1 7-6 (7-2) success.
At Indian Wells, Del Potro did not face a break point in ousting Raonic in just 65 minutes.
"I was fortunate to get a del Potro who is very, very low on fuel", Isner said.
"So that was certainly a big advantage for me. Zverev is a big server like Isner, but standing 4 inches shorter than the 6'10" Isner, plays a fairly different game. I appreciate it, even though you were cheering for Juan Martin.
"I will try to keep going and see how far I can go", Del Potro said. "There's no other way to play the point, especially for me, because I can't really run from side to side". "He's been the best player in the world for the past four, five weeks winning Acapulco, winning last week as well". I don't have any skills for that. I know better than anyone what it's costing me, all the days there is something new but I don't want to stop.
With little margin for error, Zverev lost serve and fell behind 5-4 in the final set when he dumped a forehand into the net, and his frustration boiled over.
However after taking the first set, the German was outdone by Isner, who prevailed in three gripping sets - 6-7, 6-4, 6-4.
Throughout his career, the nearly 33 year old John Isner has never won a Masters 1000 title.
GETTYJohn Isner thinks Alexander Zverev has a bright future ahead of him
Isner is the first U.S. player since Andy Roddick in 2010 to lift the Miami title.
It was the first semi-final match of the day, with the American dominating proceedings and del Potro, playing out-of-sort.
The previously unheralded Collins, a Florida native who ended 2017 ranked 167th but came into this tournament as the 93rd best player in the world, is certainly having a March to remember.
"I played extremely well".
"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. "Look, if I'm returning well and getting in return games, that should bode well for me, given how I serve", Isner told reporters after the victory.
"But with my coach, David Macpherson and I, when I first got to Miami, we have been having dinner every night and talking some things over".
If he wins 88 percent of his first-service points again, he will move to 4-0. The young German is now 3-0 in Masters 1000 semifinals. "I made some winners; made some backhand winners finally in the match and found my rhythm", said Zverev said of the breaker. "I think he's going to hit a lot of aces, a lot of winners". You've got to tell yourself to go for it.
Moscow vows to answer USA 'blackmail'; North Atlantic Treaty Organisation expels Russian staff
Skripal was granted refuge in the United Kingdom following a 2010 spy exchange between the US and Russian Federation . Stoltenberg's statement followed the earlierdismissal of more than 140 Russian diplomats from 24 different countries.