England’s late-summer series against Sri Lanka has been billed as a chance for their young players to shine: if the opening T20 was anything to go by, that is proving an accurate summation. The captain, Heather Knight, eventually made it out to the middle after bumping herself down the order to No 5, but her role was largely reduced to watcher-in-chief – only 15 runs in her partnership of 56 with Alice Capsey came off the bat of Knight.

The 19-year-old Capsey, of course, is England’s future – as she proved in the Ashes earlier this summer, and as she proved again here on a chilly evening in Hove, smashing a 26-ball half-century, her third in an England shirt. Sri Lanka’s left-arm spinner Inoka Ranaweera felt the sharp end: 22 runs off her third over, including three sixes hammered over the leg-side into the depths of the crowd.

Related: England beat Sri Lanka by 12 runs in rain-hit first women’s T20 international – as it happened

“I’ve been given the freedom to go out there and play my way, and I feel pretty settled in this group,” Capsey said. “It’s refreshing going from series to series, going into different teams and bouncing off different people’s energy.”

England are resting Nat Sciver-Brunt and Sophia Dunkley for this series, but with Capsey supported by 48 quickfire runs from Danni Wyatt and a blistering 20 off 10 balls from the 18-year-old Freya Kemp, they easily reached the heights of 186 for four – despite the match being reduced to 17 overs a side.

“We’re missing a few big names out of our squad, so it’s nice for players who have performed in regional cricket to come and get their opportunity to be a part of the England environment and see what it’s about,” Capsey said. “We have got huge depth in English cricket now.”

With Lauren Bell sitting out the first two matches of the series due to illness, there was also the opportunity for the 17-year-old Mahika Gaur (who previously represented the United Arab Emirates) to try to find her feet in ICC full-member international cricket. Left-arm seamers with the natural advantage of being 6ft 2in tall do not come along every day in the women’s game; Gaur’s debut had thus been more widely billed then most.

There have been more memorable opening overs in international cricket – this one began with a leg-side wide and ended with an unsuccessful DRS review for lbw against Vishmi Gunaratne – and when the players were forced from the field due to further rain, it looked like Gaur might have to wait another day to make amends.

Forty minutes later, though, she was handed a second chance: play resumed with Sri Lanka needing to hit a DLS-adjusted 45 runs from 17 balls. Facing up to the Sri Lankan captain, Chamari Athapaththu, Gaur got just enough away-swing to take her edge: behind the stumps, Amy Jones did the rest, and the 17-year-old had a pretty decent maiden scalp to her name.

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Two overs later, despite three successive boundaries off Kate Cross at the hands of Nilakshi de Silva, England could at last celebrate a 12-run win (via DLS). It was closer than they might have liked but a win nonetheless, amid all the chaos of rain.

Earlier, play had finally got under way at Hove an hour late, after persistent wet weather throughout the day

Wyatt continued where she had left off in The Hundred final on Sunday, sending the second ball of the innings crashing through the covers for four, before rocking back and pulling hard over the leg-side field for six more.

Although the Sri Lanka bowler Kavisha Dilhari pulled off a brilliant direct hit run-out to see off Maia Bouchier to break the 77-run opening stand, the tone for England’s dominant performance had been set.