Hales lashed six sixes in a remarkable unbeaten 64-ball 116 in Bangladesh, the final one way over mid-wicket in the last over by Angelo Mathews giving his side victory with four balls to spare after being set a huge target of 190 in the Group One Super 10 clash.
Put in to bat at Chittagong's Zahur Ahmed Chowdhury Stadium, Sri Lanka lost opener Kusal Perera in the second over but Mahela Jayawardene (89) and Tillakaratne Dilshan (55) cashed in on some dreadful fielding to steer their team to 189 for four.
England then made a woeful start to their reply, slumping to nought for two after paceman Nuwan Kulasekara removed Michael Lumb and Moeen Ali for ducks in the first over.
Hales and Eoin Morgan (57) then produced a dazzling 152-run stand for the third wicket in 15.2 overs, dragging Stuart Broad's side back into the match with some ferocious hitting.
Earlier, Jayawardene was on nought when he was lucky to be given not out by TV umpire Steve Davis after Lumb seemed to take a good diving catch at cover.
To make it worse for England, Jade Dernbach spilled a catch offered by Jayawardene on 19 and Tim Bresnan dropped Dilshan as the Sri Lankan pair forged a 145-run partnership for the second wicket.
Bresnan gave Jayawardene another life when he spilled a straightforward catch on the boundary in the 15th over.
The previously out-of-form Dilshan unfurled the famous 'Dilscoop' in the third over, bending forward to scoop a Bresnan delivery soaring over the wicketkeeper's head for a massive six.
Jayawardene was the more fluent of the two as England struggled to stem the flow of boundaries.
