"Sometimes, you hold your hands up and say you were outplayed he hit his first ball for six and we knew it was going to be a tough ask."
It was the Australians' first competitive international win in exactly 200 days and gave the team some respite after a 3-0 defeat in the recently completed Ashes test series.
Finch's swashbuckling innings overshadowed the international debut given by Australia to Pakistan-born legspinner Fawad Ahmed, who didn't take a wicket in his four overs and conceded 43 runs. Ahmed also dropped Root when the batsman was on 77.
Australia's total was the second-highest international T20 score and the 457 runs scored in the match was a T20 best. On a batsman's paradise of a pitch, England even managed its second-highest score in the format.
Finch hit paceman Steven Finn for six off his first ball and beat the ropes to reach all his landmarks.
"It was just one of those days," said Finch, who didn't feature in the Ashes series. "It is always nice to get some away early so you could get into the innings."
He reached triple figures off 45 balls two more than South African Richard Levi's T20 record but soon went past McCullum's record with a six over cover.
Shane Watson hit 37 for Australia, with Jade Dernbach grabbing figures of 3-34 for England including the wicket of Finch, who played onto his stumps.
England battled gamely after losing early wickets especially Root, who was left with a bloodied mouth by rising delivery from Hazlewood. But Finch's fireworks helped Australia to a very comfortable win only days after the Ashes series finished at The Oval.