The American dominated a second set tiebreak, eventually prevailing 6-1, 7-6 (2) in just an hour and 23 minutes to reach the fourth Masters 1000 final of his career, and his first since the Paris Masters in November 2016.
A fired up Isner yelled "Come on" and pumped his fist when he broke Chung's serve in the first set to race to a 3-1 lead, ending the Korean's streak of 27 consecutive holds of serve.The 14th-seeded Isner cruised through the remainder of the 25-minute opener, in which he fired seven of his 13 aces.
Isner, who is ranked No. 17 in the world, advances to the final of this ATP World Tour masters event at 1 p.m. Sunday (ESPN2) against the Pablo Carreno Busta-Alexander Zverev victor.
"I've been feeling exhausted in all my body for the last couple of weeks", del Potro said.
"I've played a lot of big matches where I wasn't able to free up", he said.
The win over favorite del Potro comes in a long line of surprises at the Miami Open with first Novak Djokovic, then Roger Federer, and several other top seeds-some at the hands of Isner, such as Marin Cilic a few days ago-going out earlier than expected. [ALSO LIKE] Isner broke in the third game, pounding Del Potro's backhand before hitting a forehand volley victor at net.
"I didn't think I could turn it around like this after the year I have had so far".
"Last year in the summer, I hit a run of form and was playing very well, but I wasn't beating the calibre of players I'm beating now", Isner said.
"I have been feeling tight in all my body for the last couple of weeks, but when I get into the court I love to play tennis".
"I've just continued to keep playing better", he said.
Another American, reigning U.S. Open champion Sloane Stephens, will play No. 6-seeded Jelena Ostapenko of Latvia on Saturday for the final women's title on Key Biscayne.
"I played extremely well". When he has a good day, he has everything to win a title like this.
LESSERJuan Martin del Potro of Argentina in action against Milos Raonic of Canada during their quarterfinal match at the Miami Open tennis tournament on Key Biscayne, Miami, Florida, USA, 28 March 2018. The tournament will move 18 miles north next year to the Miami Dolphins' stadium. However, perhaps tired from a tough quarterfinal clash, del Potro could do little to match the 14th seed today.