The 24-year-old all-rounder blasted eight sixes and five fours to lift the hosts to 294-7 off 50 overs after his side had been in early peril on 146-5.
Australia stuttered early and although the chase was given late impetus by David Hussey (57) and Brett Lee (57), the visitors were bowled out for 252 off 46.3 overs.
There were two wickets apiece for Andre Russell, Darren Sammy, Dwayne Bravo and Kemar Roach while Sunil Narine was miserly in claiming 1-21 off 10 overs.
The West Indies leads the five-match series 2-1 with the final match at the same venue on Sunday.
Having lost the toss, the hosts were sent in on Friday and got a brisk start through the recalled Adrian Barath (41) and local lad Johnson Charles (37).
But when Barath edged behind off McKay's bowling after hitting nine fours, Australia continued the momentum when Lee removed Marlon Samuels and left-arm spinner Xavier Doherty claimed Charles and Dwayne Bravo off consecutive balls.
When Darren Bravo (25) skied McKay into the off side, the West Indies was struggling at 146-5, but Pollard and Andre Russell fashioned a brilliant partnership of 94 off 64 deliveries.
Pollard took 49 balls for his first fifty, before exploding in the latter overs to reach his second one-day ton.
The strongly-built Trinidadian had a couple slices of luck, dropped by Peter Forrest at deep square leg when 58 and then by Doherty at short fine leg when 77. On both occasions, Clint McKay was the unlucky bowler.
Pollard arrived at his century with a disdainful pull off Lee that sailed over midwicket and into the partying crowd on the grass banks.
Sammy helped Pollard finish the innings in style, with three fours and two towering sixes in an unbeaten 31 off 13 balls.
Lee's final over of the innings cost 23 runs and included three sixes—although the fast bowler tried to make amends as he top-scored in Australia's innings.
When Michael Hussey gloved a pull down the leg side, the visitors were in trouble on 112-5, but David Hussey struck a run-a-ball half century to revive Australia and after he was bowled by Roach, Lee kept his team's hopes alive.
Lee, who was hit a hasty blow on his hand from a Roach beamer, took revenge by blasting 24 off one over from the same bowler and he notched his third one-day 50.
However, after losing Xavier Doherty and Clint McKay, Lee was last man out to Roach, holing out to long-off.
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