JOE Root struggled to sleep on the eve of England's series-clinching victory over Sri Lanka – but it did not take him long to realise he could rest easy with his fast-evolving side.

Sri Lanka resumed their innings on the final morning in Kandy needing 75 for victory, with England hunting three wickets that would put them 2-0 up and repeat an achievement last achieved by Nasser Hussain's class of 2001.

As captain Root spent his night tossing and turning as he played the permutations over in his mind, doubtless fretting over a slow pitch, a softening ball and the match-winning potential of Niroshan Dickwella.

As it was the tourists wrapped a 57-run win in half an hour, Moeen Ali striking twice in an over and Jack Leach completing a maiden five-wicket haul to bring down the curtain.

Asked how he slept Yorkshire's Root said: "I didn't. Three hours, I reckon. I was thinking about all different numbers of scenarios that could happen but as soon as I got to the ground I felt very calm.

"Knowing the ability within the dressing room, the number of different options that we can turn to, we were always going to be able to create enough chances to win the game. It was just about being cool enough to take them and we certainly did that."

Seeing off Sri Lanka on their own patch may not carry quite the same cache as it did 17 years ago, when they could call on Muttiah Muralitharan, Aravinda de Silva, Mahela Jayawardene, Kumar Sangakkara et al, but it is still a proud achievement.

They have lost only one of their previous six series on home soil, routing South Africa most recently, and were last overturned by non-Asian opponents in 2014.

For England it represents a first away success since beating the Proteas in 2015/16 and a first with Root as captain.

"It feels very special," he said. "It's about the character, the skill level and the hard work that's put in around the games. It all adds up."

There were many individual contributions to reflect well on. His own second-innings century takes some beating, but two last-wicket stands worth over 100 runs, Keaton Jennings' inspired fielding at short leg and three spinners taking 19 wickets between them all played a big part.

Root kept his focus firmly on the collective, though, and the developing identity of the team. Eoin Morgan's one-day team have become world number ones by leaning into their attacking instincts and Root has been pushing the Test squad in the same direction throughout 2018.

"We're learning from the one-day side. Eoin said to the guys 'go and play with freedom' and you saw when the guys really took that in, harnessed it, embraced it we saw a big improvement very quickly," explained Root.

"It's been a great eight months for us. It felt like we had a breakthrough moment at the start of the Christchurch Test match (in April), we sort of turned a corner.

"That was where we stripped things back a little bit and tried to give real clarity. We'd had a really tough time of it up until then that winter (losing the Ashes) and it was a real good chance for us to draw a line under it, get a clean slate and start something. Since that point I think we've really looked to continue our improvement and I think we're seeing our reward now."