Chasing an original target of 190, England's pursuit was interrupted by rain with the score on 57 for two. When play resumed after a lengthy delay, the Duckworth-Lewis-Stern method set the visitors a revised 168 from 17 overs, leaving 111 required from the final 9.4.
Jos Buttler, appearing in a record-breaking 402nd England international, had already given the chase shape with a fluent 39 from 29 balls before holing out shortly after the restart. The equation still looked steep when Harry Brook arrived, but the captain transformed the contest in a matter of minutes.
Brook launched a breathtaking assault, smashing four sixes in a 12-ball 36 to drag the required rate back under control. His innings ended when he was caught attempting an audacious scoop off Matheesha Pathirana, but the damage was done.
From there, Banton ensured England did not squander the advantage. Recovering from a difficult night in the field, the left-hander played with authority and calm, finishing 54 not out from 33 deliveries as the target came within reach. Sam Curran provided the finishing blow, launching Janith Liyanage for six in the final over to clinch victory with two balls to spare.
Earlier, Sri Lanka posted a competitive 189 for five after being sent in. Openers Pathum Nissanka and Kamil Mishara set the tone with a rapid start, but England's spinners wrestled back control through the middle overs. Adil Rashid, Liam Dawson and Will Jacks each claimed a wicket, while Jofra Archer finished with two despite a costly spell.
Pavan Rathnayake top-scored for the hosts with an aggressive 40 from 22 balls, though Sri Lanka were hampered late on by a shoulder injury to seamer Eshan Malinga, who was unable to continue after the rain delay.
England, unchanged from the opening match, now have the opportunity to complete a clean sweep in the third T20 on Tuesday, before turning their attention to the T20 World Cup opener against Nepal on 8 February.
Sri Lanka have confirmed their 15-man squad for the ICC Men's T20 World Cup 2026, backing experience at the top while making decisive calls in the middle order ahead of the tournament's start this weekend.
Left-arm wrist spinner Tabraiz Shamsi says he is committed to the Proteas despite his consultancy stint with the West Indies during the recent T20 series.
England got their T20 series against Sri Lanka off to a perfect start as Sam Curran claimed a stunning hat-trick to help secure an 11-run win on the DLS method in Pallekele.
Quinton de Kock produced a stunning innings at SuperSport Park as South Africa chased down a huge target to beat West Indies by seven wickets in the second T20I in Centurion, sealing the series with a match to spare.
