Dube has established himself as one of the most destructive middle-order batters in the IPL, scoring 350 runs at a 170-plus strike rate
Leg-spinner Akila Dananjaya returned career-best figures of 6-54 to make India stutter at 131-7 while chasing a Duckworth-Lewis revised target of 231 in 47 overs in Pallekele.
Dhoni, who scored 45, then put on an unbeaten 100-run stand with Bhuvneshwar Kumar, who made 53, to steer the team home in 44.2 overs and take a 2-0 lead in the five-match series.
India lost seven wickets for 22 runs after a 109-run opening partnership between Rohit Sharma, who hit 54, and Shikhar Dhawan, who missed out on his half-century.
Dananjaya turned on the heat with his googly as he picked three crucial wickets, including skipper Virat Kohli for four in an over, to take some steam off the Indian chase.
But ice-cool Dhoni kept the chase on track with a gutsy partner at the other end in Kumar, who had gone wicketless during his spell as the team's pace spearhead.
While Dhoni kept picking the singles and twos, Kumar was happy playing second fiddle before unleashing his power and register his maiden ODI fifty.
Earlier Milinda Siriwardana hit a gritty 58 to lift Sri Lanka to 236-8 in 50 overs after being put into bat.
Siriwardana put on a crucial 91-run sixth-wicket stand with Chamara Kapugedara, who made 40, after the hosts were in trouble at 121-5 against a disciplined Indian attack.
Fast bowler Jasprit Bumrah took four wickets while leg-spinner Yuzvendra Chahal got two.
The third match is scheduled for Sunday at the same venue.
Dube has established himself as one of the most destructive middle-order batters in the IPL, scoring 350 runs at a 170-plus strike rate
Fraser-McGurk has blasted 309 runs in seven matches for the Delhi Capitals at a strike-rate of 235.87
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