Clint McKay's hat-trick had England - chasing 228 to win - reeling on 8-3.

But a 108-run stand between Michael Carberry (63) and Eoin Morgan (53) revived them before Buttler finished it with a six and a four in the last over.

Australia had lost their last five wickets for 18 runs to fall to 227 all out, with James Tredwell taking 3-53.

The five-match series will now go to a decider in Southampton on Monday.

"Buttler is a very cool guy," said England captain Morgan. "He practises so hard at hitting at the death and that's where he comes into his own. He's one of the best in the world at it.

"Today was a great fighting win and Monday will be a final for us. It's a great opportunity to win a series with a young side."

A tense, low-scoring game was hanging in the balance when 23-year-old Buttler was joined at the crease by Ben Stokes with England on 144-6.

But the inexperienced duo showed great maturity and skill to take England to the brink of victory with a partnership of 75 in 9.3 overs.

When 22-year-old Stokes was bowled for 25 by McKay off the first ball of the penultimate over, Australia had a chance, but two singles kept Buttler on strike for the last over with seven runs required.

The tall Somerset wicketkeeper-batsman, who had successfully reviewed an lbw dismissal on eight, launched Mitchell Johnson's first ball over midwicket for six, and two balls later struck a four down the ground to finish the match.

Although Buttler was England's hero with the bat, their victory also owed a great deal to some fine new-ball bowling after Morgan won the toss and chose to field.

Steven Finn, Boyd Rankin and Stokes took full advantage of a grassy pitch offering variable bounce to reduce the tourists to 57-4 in the 14th over.

Finn had Aaron Finch lbw to the second ball of the match and Shane Watson edged Rankin through to Buttler.

Buttler showed great agility to claim a one-handed catch above his head to remove Shaun Marsh for 25 and give Stokes his first international wicket, and, when Finn then trapped Clarke lbw on the back foot for 22, England were well on top.

But the cool-headed George Bailey led the fightback as he launched Tredwell for three sixes.

He shared partnerships of 67 with Adam Voges and 85 with Matthew Wade to drive Australia to a position from which a total in excess of 250 looked well within their grasp.

But the return of Tredwell turned the tide England's way as he had Wade caught one-handed by Carberry at short third man to initiate a late collapse.

Four more wickets fell, including Bailey for 87 off 91 balls as the tourists were bowled out with 10 balls of their 50 overs remaining.

The flurry of wickets continued into the England innings as McKay tore through the hosts' top order.

Kevin Pietersen was trapped lbw, Jonathan Trott slashed an away-swinger to Finch at second slip and Joe Root edged to Watson at first slip

   It was the 34th hat-trick in one-day cricket and the fifth by an Australian.

Carberry and Morgan's steady stand hauled England back into contention but, when both fell in quick succession, followed by the wicket of Ravi Bopara, Australia were back in the ascendancy.

In a pivotal moment, Buttler was given out lbw to Watson by umpire Rob Bailey, only for Hawk-Eye to show the ball would have missed leg stump by the narrowest of margins.

Aided by the composed Stokes, Buttler made the most of his break to guide England to a vital win.

"You have to take the good with the bad," said Clarke. "England bowled well this morning and we came back well, particularly George Bailey. I'd have liked a few more runs but we recovered well.

"Clint McKay bowled really well and deserves the credit for his hat-trick, but we couldn't get over the line. You can always do more and look to get better and we'll do that."