Lewis century gifts West Indies consolation victory in Sri Lanka
Returning to 50-over matches after a three-year hiatus, Lewis left spectators at Pallekele in awe as the visitors reached their target of 195 with six balls to spare.
"He's an amazing player, it's great to see him back," West Indies captain Shai Hope said.
"He picked up where he left off. I am happy he scored some runs and I hope he can take that form into the next series."
The 32-year-old Trinidadian shrugged off the pain after twisting his ankle mid-innings to clock his fifth ODI hundred -- a vital one for a West Indies side that had struggled against Sri Lanka's spinners all series.
He hit the winning runs with a towering six off Asitha Fernando to finish on an unbeaten 102 off 61 balls with nine fours and four sixes.
Sherfane Rutherford made his third consecutive half-century in the series, already sealed 2-0 by Sri Lanka.
Together, the duo forged an unbroken 88-run partnership for the third wicket in 45 balls, showing poise and composure even as the required run rate crept above 12 per over.
Sri Lanka let several chances slip through their fingers, with dropped catches and fielding lapses that could have halted the tourists' momentum.
Successive downpours stole over five hours from the game, reducing it to a 23-over contest.
Sri Lanka had posted 156-3 before the Duckworth-Lewis-Stern method revised the chase upwards.'Weren't good enough'
"It was a bit disappointing with the way things went on today," home captain Charith Asalanka said.
"We fancied our chances when they had to chase 195. But we weren't good enough."
Kusal Mendis gave the hosts a flying start with a dazzling 19-ball fifty.
When the covers finally came off after dark, he hit four boundaries off Roston Chase in the last four balls of the over.
He twice pulled to mid-wicket, then drilled one down the ground, and deftly cut the final delivery past short third man, giving Sri Lanka the surge they needed.
Mendis then humbled left-arm spinner Gudakesh Motie with back-to-back boundaries, the second of which pushed him past 4,000 career ODI runs.
He finished on an unbeaten 56 after hammering nine fours and a six.
Opener Pathum Nissanka anchored the partnership with a composed 56 off 62 balls, before he was run out by Alzarri Joseph.
The West Indies' fielding woes continued with four dropped chances blunting their efforts.
The visitors handed 17-year-old Jewel Andrew his ODI debut, making him the youngest West Indian to play the format.