The left-hander’s unbeaten fifty seven — his fourth fifty of a tournament where he’s averaging over 100 — saw his team home once they’d been wobbling at 187 for 5.
But India reached their target of 261 with fourteen balls to spare.
Victory got wind of a dream semifinal against arch-rivals Pakistan in Mohali on March thirty.
Australia captain Ricky Ponting scored his 1st international century in over a year during a total of 260 for 6.
But it wasn’t enough to keep up his team’s bid for an unprecedented fourth straight World Cup title and fifth in all.
India, aiming for a primary World Cup title since 1983, required fifty four to win off the ultimate ten overs.
Yuvraj eased fraying home nerves with a square-driven four off Brett Lee and, with erratic speedster Shaun Tait (one for fifty two in seven overs) conceding thirteen runs within the forty first over, the target became well beneath a run-a-ball.
Yuvraj struck an excellent straight six off Tait before ending the match with a four off Lee.
He was well-supported in an unbroken sixth-wicket partnership of seventy four by Suresh Raina (34 not out).
Ponting was previously concerned during a controversial incident that may have seen Gambhir out for nought when he dived forward at sq. leg for a attainable catch before suggesting he was unsure on whether or not the ball had carried.
The umpires referred the choice however replays showed the ball bouncing well in front of Ponting.
Opener Sachin Tendulkar looked in elegant bit.
But Australia denied him his one hundredth international hundred when he was caught behind off Tait for a fluent fifty three throughout that he became the primary batsman to attain eighteen,000 one-day international runs.
Gambhir and Virat Kohli batted steadily during a stand of forty nine before Kohli (24) slapped a full toss from part-time spinner David Hussey straight to Michael Clarke at short mid-wicket.
Now the question was may the remaining batsman avoid panic.
Unfortunately for India, left-hander Gambhir could not.
One ball once surviving a run-out, he set-off for a non-existent single and was well-beaten by Cameron White’s throw to David Hussey having created fifty and been during a position to win the match for India.
Instead, at 168 for four, the pressure was back on India which solely increased when skipper MS Dhoni fell for seven once a stop Lee was well caught by a diving Clarke at purpose.
Earlier, Ponting’s 104 was his 1st hundred since he created 106 against the West Indies during a one-day international in Brisbane last year.
Ponting, who’d managed simply 102 runs at twenty.4 in 5 previous innings this tournament, had return into the match amidst reports he may be quitting international cricket utterly once the planet Cup.
Nevertheless the 36-year-old demonstrated his enduring category during a 118-ball innings that includes a six and 7 fours.
He was out late on when he reverse-swept Ravichandran Ashwin straight to Zaheer Khan at short third man.