Joe Root returned to form with a fluent 93 to lead England to a crushing 122-run victory over Sri Lanka in the fifth and final one-day international in Cardiff on Saturday.

Root, short of runs in the test series which England won 2-0, shared a 109-run fifth-wicket stand with Jos Buttler to lift the hosts to 324 for seven from their 50 overs.

David Willey took four wickets and Liam Plunkett three as England bowled out Sri Lanka for 202 to win the one-day series 3-0.

"I'm a very happy captain. We've put in probably our most convincing performance of the series," England's Eoin Morgan told reporters.

"We've got better throughout the series but we've grown together and got closer as a side."

Jason Roy (34) and James Vince (51) put on 67 for England's first wicket and Morgan made 20 and Jonny Bairstow 22 to keep up the momentum before Root and man-of-the-match Buttler, who struck 70 off 45 balls, powered the side to a commanding total.

Sri Lanka lost wickets at regular intervals, only a defiant 48 from Dhanushka Gunathilaka and 53 by Dinesh Chandimal holding up England, who dismissed the tourists in the 43rd over.

"We've been having the same problems over the last five weeks. Either batting, bowling or fielding has let us down," Sri Lanka captain Angelo Mathews said.

"We needed a perfect performance to beat England but they played very well."

The teams meet in a one-off Twenty20 international in Southampton on Tuesday.