It was the second-biggest defeat by run-margin in the tournament history after Namibia's 256-run loss to defending champions Australia at Potchefstroom in South Africa in 2003.
Sri Lankan skipper Mahela Jayawardene (85), Kumar Sangakkara (76) and Chamara Silva (55 not out) feasted on a mediocre Bermudian attack to help their team post a challenging 321-6 after electing to bat.
Bermuda were then clueless against Sri Lanka's seamers before being dismissed for an embarrassing 78 in just 24.4 overs, the sixth lowest ever World Cup total.
Farveez Maharoof finished with 4-23, while Lasith Malinga grabbed three wickets with his deceptive round-arm action. Off-spinner Muttiah Muralitharan took two wickets.
Lionel Cann (28) and David Hemp (14) were the only batsmen to reach double-figures in a dismal Bermudian batting performance.
India and Bangladesh are other sides in Group B, with the top two advancing to the next Super Eight stage.
Bermuda looked in the fray for a brief spell in the morning when they dismissed veteran Sanath Jayasuriya and Upul Tharanga in the space of 14 runs to reduce the 1996 champions to 78-2.
They opened the Cup with an erratic eight-ball first over, sent down by Kevin Hurdle who also rapped Jayasuriya on the knuckles with a rising ball.
Then they dropped Jayawardene first ball. The lapse proved costly as the Sri Lankan captain went on to make 85.
It soon became an ordeal in the sun for the Cup debutants as Jayawardene, Sangakkara and Silva all made merry with their rich stroke-play. At no stage did they look like containing Sri Lanka to a modest total.
Bermuda held three superb catches, including two by Janeiro Tucker, but also dropped one more and sent down as many as 14 no-balls and 13 wides.
Jayasuriya, playing in his fifth and last Cup, needed on-field medical attention but soon overcame the pain. He went on add 62 for the opening wicket with Tharanga (30) before being caught cutting at point off Saleem Mukuddem.
Mukuddem nearly got a second successive wicket, but burly Dwayne Leverock grassed a regulation catch at lone slip to let off Jayawardene. The Sri Lankan captain got another 'life' when he was dropped on 51 by the same fielder.
Sri Lanka lost their second wicket when Tharanga was caught down the leg-side by wicket-keeper Dean Minors, but Jayawardene and Sangakkara restored normalcy with a 150-run stand for the third wicket.
Jayawardene and Sangakkara exposed Bermuda's bowling limitations with their impressive knocks, scoring comfortably against both pace and spin. When Sri Lanka lost the third wicket, they were already in a strong position.
Sangakkara struck six fours in his 37th half-century before he fell in a bid to step up the run-rate. He attempted a big shot off spinner Leverock and was caught by Tucker, who took a well-judged running catch at the boundary.
Jayawardene hit two sixes and six fours in his chancy half-century before falling to superb diving catch by Hurdle at deep mid-wicket.