Watson, 25, picked two wickets to help skittle the Caribbeans for 138 and then stroked 57 not out to reach a revised target of 116 following rain.
The Queenslander was named the player of the final.
"My goal was to get through to the end," he said. "One of the dreams, you wish you hit the winning runs for your country."
Watson is in the race for the number six slot in the team along with Michael Clarke and Andrew Symonds as Australia seek to avenge last year's Ashes defeat in England.
His chances look promising due to the flexibility he can provide when the series starts in Brisbane on Nov. 23.
"I've loved the opportunity of batting at the top order," he said. "With so many greats coming below me, it is quite easy to set a good platform."
Watson also scored 50 braving cramp against India. He tallied eight wickets in the tournament.
"It has been a great challenge to bowl here," he said. "Contributing to the team's victories has been very important." He has provided crucial breakthrough with his ability to extract bounce on slow Indian pitches.
In the group A victory over England, it was Watson who removed Ian Bell to end his 83-run opening stand with Andrew Strauss, finishing with three wickets and scoring 21.
However, his technique as opener was questioned after he was out playing the pull shot -- bowled by England's James Anderson and miscuing Kiwi seamer Kyle Mills to mid-off in the last four.
Skipper Ricky Ponting defended Watson's talent after the semi-final and coach John Buchanan advised him to cut out the risky shot early in his innings.
Watson kept his promise on Sunday, focussing on drives and placements and showing great patience to build the innings.
"I just have to stick to a simple plan and make sure I bat through the innings," he said. "Today I learnt a lot, which I'll take on board and use for the next one-day tournament."
