Despite a fighting half-century from Rahul Tripathi (58 from 37 balls), they eventually folded out for 125 in 19.2 overs with Wanindu Hasaranga claiming five wickets for 18 runs.
The Sri Lankan was ably supported by the pace trio of Akash Deep (3/45), Harshal Patel (2/11) and Mohammed Siraj (1/25) after RCB won the toss and elected to bowl at DY Patil Stadium in Mumbai.
Sri Lanka all-rounder Wanindu Hasaranga will miss the upcoming T20I series against India after testing positive for COVID-19.
The hosts may have beaten West Indies 3-0 in the shortest format but their struggle against spin — a trend that’s become hard to ignore in recent times — refuses to abate.
Dasun Shanaka praised his team for a complete performance that help them beat defending champions West Indies by 20 runs.
Going into the game with two losses in three games, the West Indies were always up against it and Sri Lanka out-batted them by amassing 189 for three on a good batting surface.
Sri Lanka's chase too started on a disappointing note as they lost their first three wickets with the scoreboard reading 34 runs in 5.1 overs.
For Sri Lanka, Wanindu Hasaranga was the most successful bowler with figures of 3/21.
Chasing 143 for victory, South Africa reached the target with one ball to spare in their Super 12 Group 2 match, in which Wanindu Hasaranga de Silva also picked up a hat-trick.
Sri Lanka, who had won the title in 2014, topped group A with three successive wins before outwitting Bangladesh by five wickets in their first Super 12 match.
Wanindu Hasaranga, Pathum Nissanka star in Sri Lanka's massive 70-run win over Ireland in T20 World Cup
Wanindu Hasaranga's rearguard fifty was beautifully complemented by a clinical bowling display as Sri Lanka sealed their place in Super 12s.
Hasaranga and Chameera were roped in as replacement players for Australians Adam Zampa and Daniel Sams by the franchise ahead of the second leg of the ongoing season.
With just two days to go for the Players Draft in the Abu Dhabi T10, Deccan Gladiators have retained Sri Lankan leggie and explosive batter Wanindu Hasaranga in the squad.