England v Sri Lanka: Third T20, Derby
England 116 (19 overs): Bouchier 23 (18); Athapaththu 3-21
Sri Lanka 117-3 (17 overs): Athapaththu 44 (28); Glenn 2-23
Sri Lanka won by seven wickets
England suffered a shock first-ever series defeat by Sri Lanka as the tourists won the third T20 by seven wickets at Derby.
England were bowled out for 116 in 19 overs after another impressive Sri Lankan performance in the field.
Chamari Athapaththu top-scored with 44 from 28 balls as Sri Lanka reached their target with three overs to spare.
It is only Sri Lanka's second series victory from their last 15 bilateral series.
Athapaththu was dismissed by Alice Capsey with 52 runs still required but Harshitha Samarawickrama and Hasini Perera played sensibly to withstand England's economical bowling to complete the chase.
It is England's second successive batting collapse after their 104 all out in the second T20 at Chelmsford, with Heather Knight's side looking fatigued and short of answers to Sri Lanka's spinners.
They started poorly again and failed to recover as Danni Wyatt was caught at cover from the first ball of the game before Capsey was calamitously run out in the second over after a mix-up with Maia Bouchier, who went on to top score with 23.
Sri Lanka's players were visibly emotional, running on to the pitch and embracing the batting pair as the winning runs were struck.
Meanwhile, England will look to fight back in the three-match one-day international series, which starts in Durham on Saturday.
A chastening night for England
England's selection for this series has been a big talking point, the hosts missing some key players like Nat Sciver-Brunt and Sophia Dunkley, and Sophie Ecclestone and Lauren Bell later ruled out by injury and illness.
Sciver-Brunt, however, played domestic cricket for her regional side The Blaze last weekend, though she is expected to return for England in the 50-over format.
Players did need the rest - England's Ashes summer was hectic, followed by a jam-packed Hundred in August, but despite missing that experience, England are not expected to lose to Sri Lanka.
England's professionalism and strength in depth is far superior to their opponents, and there are still many experienced players in their squad - but it was their lack of clarity with the bat and repeated mistakes from the second T20 that should frustrate them.
They looked lost against spin, constantly opting for ambitious sweeps and reverse sweeps against the loopy slow bowling that Sri Lanka expertly used to tie them in knots.
Their most experienced duo of Knight and Amy Jones were tasked with steadying the ship - finding yourselves three wickets down with an inexperienced batting line-up can be forgiven.
The pair led a brief recovery with fourth-wicket stand of 29 but both succumbed to spinners again as the middle order lost three wickets for just two runs, leaving number seven Danielle Gibson to rescue England with a sprightly 21 from 15 balls.
England may not admit complacency, but in the selection, it appeared as if they underestimated their opposition.
It is also possible that after their summer, it may have been a series too far after the high of such a promising Ashes campaign.
But regardless of the reason, England's next World Cup challenge comes in Bangladesh in 2024 and it would be no surprise to see opposition teams stacking their line-ups with spinners after the past two outings.
Athapaththu leads from the front again
Few were expecting Sri Lanka to win a game in this series, given the teams' rankings and England's impressive Ashes performance, but they were inspired by their captain Athapaththu after a heavy defeat in the opener at Hove.
It was going to take something special to inflict a first series defeat on England by a team other than Australia since 2010, and the captain managed it.
Athapaththu, by far Sri Lanka's most experienced player having played in their first ever T20 in 2009, took 3-21 in England's collapse and swaggered to the crease with a purpose to begin their chase.
She backed up her half-century at Chelmsford, getting her side off to a flyer with a six off Kate Cross in just the second over.
Breaking the back of the chase was important in allowing the side's less experienced middle order to do the rest with simple, risk-free cricket - and they played with a smartness that England didn't.
Sri Lanka looked the more professional side particularly in the field, bowling to their strengths with spin, taking all their catches and playing as a unit, sharing each others' joy as wicket after wicket tumbled.
England started the summer with packed crowds at Edgbaston, Lord's and The Oval with an unlikely series victory over Australia, but at Derby, they went down with a whimper.
For Sri Lanka, though, this marks history. They will look to improve in the ODI series but they are playing with nothing to lose after already exceeding expectations.
'A valuable lesson for us' - what they said
Former England spinner Alex Hartley on BBC Two: "We all said it would take something very special for Sri Lanka to come here and win one game, so to come out and win a series is testament to how they have stayed positive after the first defeat and put England under so much pressure.
"Was there a bit of complacency from England? I'm not sure. They did rest their big guns, but they have got a lot of lessons to learn."
Former Sri Lanka all-rounder Russel Arnold on BBC Two: "It has been so impressive because it is not easy coming here to play. It is the first tour for a lot of them here.
"Yes, England have rested some players but this is still a quality side with highly-skilled players in their line-up.
"The fightback after losing the first T20 is particularly impressive."