Australian #NextGen star Nick Kyrgios overturned a 0-2 FedEx ATP Head2Head mark against the top seed.
He prevailed over him 7-6(3), 7-6(4) in one hour and 47 minutes.
Second seed Kyrgios stopped Isner’s 15-match winning streak in Atlanta and ended the big-serving American’s quest for a historic four-peat at the hard-court event.
He also improved to 2-1 in ATP World Tour finals, adding to his title on the indoor hard courts of Marseille in February.
“I knew it was going to be tough from the get-go,” said Kyrgios. “John is still so comfortable on that court.
“I needed to come up with some special stuff today and it just came down to a couple points here and there.
“I did all the right things today and stayed calm. I knew I’d have my chance.
“In Marseille, I was unbeatable. This week was completely different.
“I wasn’t playing well at all at the start of the week. I wasn’t in a good space at all.
“Some things just fell my way. Today, I found the right balance. I was competing and had some fun.”
Conceding an early break can often be challenging to recover from. Against Isner, it can be devastating.
Kyrgios had his back against the wall at the start, facing three break points at 0/40 in his opening service game.
The 21 year old would save them all, reeling off five straight points to earn the clutch hold.
“Returning is very crucial against John,” said Kyrgios. “That serve is world-class.
“It would have been a completely different story if he got me there.”
Isner would save a break point at 3-all with a mammoth service winner and another two games later with a deft volley winner.
But the sweltering, humid conditions would take its toll on the 6’10” American.
Visibly fatigued, a physically labouring Isner would fall behind a quick mini-break in the ensuing tie-break, and Kyrgios would clinch the opener with an ace up the T.
The Aussie fired 13 winners and overcame 92 per cent first serve points won by Isner in the first set.
His movement significantly compromised by fatigue, Isner looked to be on the ropes as the second set got underway.
But the three-time champion got a second wind as cloud cover crept over Atlantic Station.
With rain on the horizon and rumbles of thunder in the distance, they would exchange mini-breaks in the ensuing tie-break, before Kyrgios clinched the victory on an Isner double fault.
Kyrgios ended the American title stranglehold in Atlanta, with Mardy Fish, Andy Roddick and Isner combining to win all six previous editions.
He earns 250 Emirates ATP Rankings points and $109,950 in prize money.
He’s projected to rise to a career-high World No. 16.
The Canberra native had lost to Isner at ATP World Tour Masters 1000 tournaments in Madrid and Montreal last year.
Isner was bidding to become just the fifth active player to win four consecutive titles at an ATP World Tour event, along with Novak Djokovic, Roger Federer, Rafael Nadal and Kei Nishikori.
He has appeared in the Atlanta final in six of the tournament’s seven years in existence, also finishing runner-up to Fish in both 2010-11.
Isner takes home $57,910 in prize money and 150 Emirates ATP Rankings points.
“It was an encouraging week for me,” said Isner. “It was my first final since here last year.
“It’s tough to make a final. The guys are good out there. It’s definitely been an encouraging week.
“The margins in my matches are pretty small and I just have to fix some things. Of course I wanted to win this.
“I love the event. But I’m not too discouraged. I know I’m not far away and these close matches will start going my way.
“When the sun was out, I was struggling. It was really hot out there. I hadn’t played under the sun at all.
“It was an adjustment. I go back to that second game of the match. He came up with really good serves.
“He’s one of the best servers on the tour, with a very fluid motion.”
(c) Copyright 2015 www.sportmo.com; like our Facebook page: “Sportsmo”. Drop your comments below: