Put into bat, the famed Indian batting line-up, bolstered by the return of opener Virender Sehwag, produced a spineless display as the top half was back in the hut by the 11th over before Raina did the rescue act on a batting track at the Sher-e-Bangla National Stadium.
The left-hander, who struck 10 fours and a six in 115 balls for his third ODI hundred in 87th match, shared a 106-run sixth wicket partnership with Ravindra Jadeja (38) to revive the innings which eventually folded in 48.2 overs.
The Indian innings ended without a final flourish after Raina was out in the 46th over with Harbhajan Singh (11), Zaheer Khan (16) and S Sreesanth (4) returning in quick succession as the tail failed to wag.
For Sri Lanka, pacers Nuwan Kulasekara and Chanaka Welegedara, who damaged the Indian top-order, took four and three wickets respectively.
Coming at the fall of captain Mahendra Singh Dhoni when his side was tottering at 47 for four in the ninth over, Raina kept one end intact grafting for runs initially before opening up later.
Jadeja also did the right thing, staying put at the crease and giving company to Raina for 23.4 overs.
While their illustrious colleagues, with the exception of Sehwag (42), fell cheaply to loose shots, the duo played the balls on merit and waited for a final flourish at the slog overs which though did not come. Gautam Gambhir and Yuvraj Singh were out for ducks while Dhoni and Kohli could contribute 14 and two respectively.
After Jadeja was out in the 35th over, Raina played some delightful shots, including a six of promising off-spinner Suraj Randiv. He raised his hundred with a two off Thissara Perera in the 44th over with the help of nine fours.
The Sri Lankan bowlers used the early life on the pitch with some swing and bounce but it was more due to the Indians rushing for shots, in search for quick runs to post a big total to cancel out the dew factor when they bowl later, which led to their downfall.
Seamers Kulasekara and Welegedara made early breakthroughs though they were a tad expensive due to some punishment from Sehwag. India had the worst start in the tournament with opener Gambhir and in-form Kohli back in the pavilion by the second over.
Gambhir missed completely an inswinging Kulasekara delivery which disturbed his leg stump after caressing the thigh pads and India were one for one.
In the next over, Kohli perished while trying to slash a wide delivery off Welegedara to offer an easy catch to Kumar Sangakkara. Sehwag, however, seemed unperturbed as he punished Kulasekara for three fours in the third over but new man in Yuvraj made a quiet exit without opening his account.
Yuvraj chased a Welegedara delivery for a cut without moving his feet and Thilan Samaraweera took a smart catch in the slips as India slumped to 16 for three.
Sehwag and Dhoni tried to revive the innings with a brief 32-ball 31 runs for the fourth wicket before the Indian captain nicked Kulasekara to Sangakkara in the ninth over while going for a drive. Sehwag continued to plunder runs, hitting Welegedara for two fours to take India score to 58 for four after 10 overs. But it was not to be his day and Indian hopes of a recovery virtually ended with Sehwag's dismissal in the 11th over for a 27-ball 72 which contained seven fours.
Sehwag went for an upper cut and the edge ended safely on Sangakkara's gloves to the disappointment of 5000-odd Bangladeshi spectators who cheered at every shot of the dashing Indian opener.
Their back against the wall, youngsters Raina and Jadeja stuck to the wicket and played the balls on merit scoring occasional boundaries. But just India looked like they have reached a stage from where they could launch for a defendable total, Jadeja was out LBW to a Tillakaratne Dilshan ball which straightened after pitching on the middle stump.
