SL vs ENG: Clean Sweep For Sri Lanka In Tests By 2-0, England Beat Host By 6 Wickets
Sibley and Buttler put on an unbeaten 75-run stand as England, who were struggling at 89-4, got to their target of 164 in an extended final session on the fourth day in Galle.
The result gave England a second successive Test whitewash in Sri Lanka after winning all three matches in the island nation in 2018.
England were given a deadline to finish in the day after spinners Jack Leach and Dom Bess skittled out Sri Lanka for 126 in their second innings.
Left-arm spinner Lasith Embuldeniya claimed three wickets that gave Sri Lanka hope and helped him to his Test-best match figures of 10-200.
Debutant spinner Ramesh Mendis got the key wicket of skipper Joe Root, who scored 11 after his 186 in England's first innings total of 344, to add to the scare given to the tourists.
Embuldeniya took Zak Crawley for 13 and then ended Jonny Bairstow's stay after a quickfire 29, putting England's nerves on edge, but Sibley calmly moved to his third Test half-century.
Leach and Sibley took four wickets each to set up England's win.