The classy batsman hit six fours and four sixes in his 44-ball knock as England finished on 230-8 with two balls to spare after South Africa made 229-4 in their World Twenty20 clash in Mumbai.
It was England’s highest ever total in 20-over cricket and the highest successful run chase by any team at the World T20.
It was also the second-best ever chase in the history of the shortest format of the game.
“There’s no better feeling than winning a game of cricket when you’re up against it,” said Root.
“It’s massive. The fact we can pull performances like that out with the bat gives us lots of confidence in the group stages and hopefully further in this tournament.”
The 25-year-old said his innings at Mumbai’s Wankhede Stadium was “definitely” his best ever in short-form cricket, adding that to do it in a world championship was “very special”.
England went into the last over needing just one run to clinch victory and Chris Jordan looked like he’d done it when he smashed the ball high towards to the boundary.
But it came up just short and was caught by JP Duminy.
David Willey was then run out for nought as a nervy England tried to clinch victory with a quick single.
Then on the third-last ball, Moeen Ali dramatically hit the winning run to ensure England bounced back from their opening six-wicket defeat to the West Indies on Wednesday.
Root said he had earlier told Ali just to “stay calm”.
“I said ‘remember the bowler is under more pressure than you at this stage’. Just stay nice and relaxed’, and thankfully he managed to get us across the line,” explained Root.
Root stylishly clinched his half century with a delightful reverse scoop which went for six in the 15th over before being caught out in the 19th over.
Opener Jason Roy had earlier scored 43 while Jos Buttler made 21 and Alex Hales 17 in the Super 10 Group One game.
Quinton de Kock, Hashim Amla and JP Duminy made half centuries as South Africa posted 229-4 after England won the toss and elected to field first.
– England’s ‘anchor’ –
England’s previous best T20 total was 214 against New Zealand in 2013 and the odds looked stacked against them.
“We definitely would have backed ourselves defending 229, but you have to give credit where credit’s due,” Duminy told reporters afterwards.
“Yes we didn’t bowl as well as we would have liked but they batted outstandingly, especially the first six overs,” as England raced to 89 for three.
Duminy also heaped praise on Root.
“He’s always had that demeanour about him, that calm head, assessing the situation pretty well and he’s been the anchor in their team no matter what format,” said the all-rounder.
England’s total was the second highest-ever run chase in all T20 cricket after the West Indies scored 236 against South Africa in January 2015.
“Honestly, I felt we would have felt to play out of our skin to chase them,” said England captain Eoin Morgan.
“But there’s a lot of talent in our team if we play with freedom. Batsmen are finding different ways of scoring,” he added.