Bermuda started brightly as Malachi Jones, at 17 one of the youngest cricketers in the tournament, struck with his first delivery when he had opener Robin Uthappa caught by burly Dwayne Leverock.
But the celebrations were short-lived as Sehwag, who had just one half-century in his previous 14 games, smashed 114 runs off 87 balls with three sixes and 17 fours for his first century in two years.
The 28-year-old opener shared a 202-run stand for the second wicket with the in-form Ganguly as India took a stranglehold on the match.
Ganguly, who scored 66 in his team's below-par batting performance against Bangladesh, looked set to become the first batsman to score five centuries in the World Cup when he was stumped attempting a big shot on 89.
India 413-5 v Bermuda, March 2007
Sri Lanka 398-5 v Kenya, March 1996
India 373-6 v Sri Lanka, May 1999
West Indies 360-4 v Sri Lanka, October 1987
Australia 359-2 v India, March 2003
Australia 358-5 v Netherlands, March 2007
South Africa 353-3 v Netherlands, March 2007
Zimbabwe 340-2 v Namibia, February 2003
Pakistan 338-5 v Sri Lanka, June 1983
Australia 334-6 v Scotland, March 2007
India, keeping an eye on the net run-rate after the loss to Bangladesh, sent in big-hitters Mahendra Dhoni and Yuvraj ahead of Tendulkar, and the move paid off as runs came thick and fast.
The Indian innings contained 18 sixes, with Yuvraj hitting seven in his 46-ball knock and Tendulkar four from his 29-balls.
Left-handed David Hemp, who plays for English county Glamorgan, top-scored for Bermuda with a solid 76 not out, but the only other notable contribution came from Dean Minors with 21 as they were all out by the 44th over.
"There will be plenty more upsets in this World Cup"
Matt, Dublin, Ireland
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Anil Kumble and Ajit Agarkar both took three wickets after Zaheer Khan's pace and swing had accounted for the openers with just 18 runs scored.
The victory was the biggest in one-day internationals by one run, the previous highest was Australia's 256-run win over Namibia in the last World Cup in South Africa.
India now need to beat Sri Lanka in their last Group B match on Friday to give them a chance of qualifying for the Super Eight stage.