Joe Root helped himself to an unbeaten century in St Lucia as England piled up a 448-run lead on day three of the third Test against the West Indies.

Root managed just 55 in his five previous innings on tour but ended the series on a high, closing day three unbeaten on 111.

England's innings of 325 for four was comfortably their best, and longest, of the tour and although there were more disappointments for openers Rory Burns and Keaton Jennings, a bright 69 from Joe Denly offered cause for cautious optimism.

Root's ton was his 16th in Test cricket – enough to put him level with Michael Atherton, Graham Thorpe and Herbert Sutcliffe – and his fifth overseas, a reminder that despite his recent wobble he remains the bedrock of England's batting.

With Windies seamer Keemo Paul injured inside the first 20 minutes and slow over-rates the issue of the day, the gentle spin of Roston Chase and Kraigg Brathwaite bowled 43 overs between them from which Root happily milked 56 of his runs.

The tourists began the day looking to build on what was already a strong position, 142 ahead thanks to Mark Wood's exploits with the ball, and with all 10 wickets intact.

Things remained that way for just a few seconds, Burns flicking Paul's first ball of the day to square leg to depart for 10. That lowered the Surrey captain's average to exactly 25 from six Test appearances, a disappointing return for such a capable player but one that is unlikely to bring a premature end to his opportunity.

The same is probably not true of Jennings, who clung on for 99 balls and 23 runs as he attempted to dig out a score of note. In the end he was bowled in ugly, if unfortunate, fashion after Alzarri Joseph's delivery took a detour off his thigh pad. He averages a fraction more than Burns from his 17 caps but does not currently have the confidence or tempo to continue at this level.

Had Denly been held by Shimron Hetmyer on 12, Gabriel the unlucky bowler having rattled the shoulder of the bat, his place might also have been in doubt.

As it was he used his extra life to showcase a pleasing line in cover drives and an ability to find the gaps behind square on the off side. After reaching lunch on 45 he brought up his fifty in style, lifting four over mid-on then crunching Kemar Roach down the ground.

Denly did not look the part on debut as an opener in Antigua but he was beginning to carry himself with conviction when he erred, wafting twice away from his body at Gabriel. He failed to make any contact the first time but got a thin edge when he tried again.

His angry reaction told the story of a job only half done. He will have known there were more runs to be had in the afternoon, 60 of them comfortably banked before tea by the fourth-wicket partnership of Root and Buttler.

Both batsmen brought up their half-centuries early in the evening, Root in 120 balls and Buttler in 10 fewer, but a brief delay when a beach ball emerged on the outfield suggested their important accumulation work was not keeping everyone's attention.

It took the new ball to part them. Roach nipped one in at Buttler but he misread the line entirely, playing inside and losing his off stump.

Joseph helped Root to three figures, providing a full toss which the skipper gratefully punched to the ropes, while Ben Stokes was 29 not out at stumps.