Joe Root is relieved to have started what he believes will be a defining year in his England captaincy by scoring his first Test hundred for 13 months.

With home and away series against India and an Ashes tour to Australia all hovering into view, Root had called on the team to start with a bang against Sri Lanka - and demanded the same of himself.

The bowlers did their part by rolling over the hosts for just 135 on day one, a total that Root overhauled all on his own as he cruised to 168 not out on Friday.

That represented over half of the team's stumps total, 4-320 and provided the bulk of a towering 185-run lead.

Having not reached three figures since December 2019, the wait for an 18th Test hundred had gone far enough and the drought ended in a style as he defended strictly, swept with authority and compiled England's record score on the island with a disarming ease.

"I'm extremely pleased, I did a lot of talking before the game and ahead of this year I thought it was really important to go out there and do it myself," Root said.

"It felt like a long time coming and now I've got to build on this, really make it count. I want to make it as big as possible and drive this first innings lead as high as we can.

"When I was a little bit younger on previous trips I might have tried to play too many shots to the same ball. One thing I was really pleased with today was my shot selection.

"I felt I got a really good combination of defence and attack. Being a bit more ruthless, a bit more stubborn and trusting my defence a little bit more at times has certainly paid off this week."

Root's conversion rate from 50 to 100 has often dogged him as a weakness but even taking lunch on 99 not out did not throw him off here.

It is a problem many players across the world would love to experience and one Root is trying not to indulge any more.

"For the last year, two years, I've over-thought it massively. I've tried to get away from that," he said.

"I've made too big a deal of it in my own mind, hyped it up, and probably because of that it's been to my detriment.

"Generally when I do get to hundred I make it really count so tomorrow I'm trying to make that another really big one."

The last time Root scored a Test ton, against New Zealand in Hamilton 13 months ago, he went on to turn it into 226, a fate that Sri Lanka must fear on Saturday.

"We want to put them under pressure and bat just once," Root said.

He shared a fourth-wicket stand of 173 with debutant Dan Lawrence, who provided exactly 73 of them in what was a dashing first outing in international cricket.

"I was very impressed, I thought he played magnificently well," said Root.

"He showed exactly why he deserved his opportunity to play and it's the start of something very special for him."