Triangular one-day international series, Colombo:
Sri Lanka 307-6 (50 overs) beat India 168 (37.2 overs) by 139 runs
Mathews completed the first six-wicket haul of his career
Seamer Angelo Mathews took 6-20 as Sri Lanka thrashed India by 139 runs in the triangular one-day series in Colombo.
Both sides had already qualified for Monday's final after both beat New Zealand earlier in the tournament.
Opener Sanath Jayasuriya had blazed a trail for Sri Lanka with 98, while Thilina Kandamby smashed 91 not out from 73 balls in Sri Lanka's 307-6.
Rahul Dravid made 47 for India, who collapsed from 105-2 to 168 all out as Mathews played the starring role.
The run chase had begun brightly but both openers failed to build on a good start as Dinesh Karthik was caught behind off Thilan Thushara for 16 and Sachin Tendulkar hit five fours before he holed out off Nuwan Kulasekara for 27.
Dravid and Yuvraj Singh added 38 before the latter was caught behind off Lasith Malinga - and that was the cue for Mathews to run riot, claiming six of the last seven wickets to fall - four of which were bowled.
Earlier, veteran left-hander Jayasuriya, whose place had been under threat, showed he had lost none of his class as he punished India's new-ball seamers to reach his 68th one-day international fifty, although he was trapped lbw by Ashish Nehra just short of a 29th ODI century.
Sri Lanka were 176-5 with 19 overs remaining but Kandamby punished a flagging Indian attack and came close to a maiden international hundred.
"No matter the result today, we still have to turn up on Monday and do the same thing if not better," Sri Lanka captain Sangakkara said.
"It was great to see Sanath returning to form. We expected that at some point and it's pleasing that it came sooner rather than later.
"Angelo Mathews is an all-rounder we have been looking for and we hope he keeps going and cements his place in the side. He's got a great future and I'm sure he will not let this early success get to his head."
Meanwhile, India skipper Mahendra Dhoni conceded: "The only thing that went right was the warm-up session.
"We then lost the toss and everything else went haywire."