Lankans, who were in firm control of the proceedings from start to finish, eventually eased past the target with well over 15 overs to spare.
Indian batsmen failed to negotiate the new ball bowlers' swing and had no answers for the teasers posed by spinners Mendis and Murali as hosts were bowled out for paltry 146 in 46 overs. In reply Lanka, despite losing both the openers cheaply, made short work of the small target, thanks largely to the responsable knocks from Mahela Jayawardene (61* off 82) and Chamara Kapugedera (72-ball 45*).
Dhoni used as many as seven bowlers but Lankan skipper Mahela and Kapugedera succeeded in thwarting all attempts. Only Munaf looked penetrative but not threatening enough to wrest the game away from Lanka.
Earlier, Lankan new-ball attack Vaas and Kulasekara (2/23) started the rot dismissing the three top-order batsmen cheaply.
Spinners Mendis (3/21) and Murali (3/37) then ran thro the middle and lower order to leave the insipid India reeling on 87/7. However some late slurry from tailenders helped India post a respectable total.
Indian top-order barring Gambhir got the starts but failed to capitalise on it. The young Indian batsmen had neither the technical correctness nor the stomach to survive against the formidable Lankan attack.
India sans Sehwag, opting to bat, got off to a disasterous start losing the in-form Gambhir in the very first over of the innings. The Indian southpaw played a length ball from Vaas across the line and paid the price. The rookie seamer Kulasekara got into the act removing the debutant Virat Kohli (12) and Raina (17) as India slumped to 36/3 in the 12th over.
Yuvraj (23) and Rohit (19) steadied the tottering Indian innings with a 37-run stand. Yuvraj looked comfortable at the crease when seamers were operating. He cut and pulled to fence and lofted Mendis for a six before the unorthodox struck back with a quicker one to disturb the timberwork of the Indian swashbuckler.
Rohit, who was content milking the ball in gaps for singles and twos for his 31-ball 19, followed Yuvi to the pavilion when he edged a short of length delevery from Thushara straight into the safe pair of hands of Lankan skipper Jayawardene.
Dhoni and Irfan Pathan came and went in a jiffy to leave India in a spot of bother at 87/7. However the tailenders chipped in with some useful runs to ensure a respectable total for India. Ojha remained unbeaten on 16. Munaf scored a run-a-ball 15. Harbhajan and Zaheer made 12 apiece.
Lanka take 1-0 lead in the five-match ODI series. The teams will play the second ODI in the same on Wednesday.