Sam Curran took the key wicket of centurion Lahiru Thirimanne as Sri Lanka continued to chip away at England's lead in the first Test at Galle.

Thirimanne led a spirited fightback on day three and dug in again to turn his overnight 76 not out into a hard-fought 111. Despite his departure the hosts moved on to 242 for four at lunch, just 44 behind and in with a chance of making things difficult in the fourth innings.

With spinners Dom Bess and Jack Leach again underwhelming with too few genuinely dangerous deliveries and too many short ones, it fell to Curran to make the breakthrough with the second new ball.

Coming round the wicket the all-rounder found a hint of swing and seam to take the inside edge, narrowly avoiding chopping on only to be caught behind by a diving Jos Buttler.

It had been a memorable stay for Thirimanne, just the second Test hundred in his 37th appearance and the first in over seven years, and an important one in the context of an increasingly tight contest.

Things had started well for England, with Bess dismissing nightwatchman Lasith Embuldeniya for a duck in the second over of the day, Dom Sibley holding a gentle push at short cover. The off-spinner was unable to capitalise, though, finding Thirimanne a particularly thorny opponent.

On four separate occasions the left-hander felt able to rock on to the back foot and cut Bess for four, the first drawing an unsuccessful dive from Sibley and the last bringing up his long-awaited century. Leach's left-arm spin was not quite as loose but he was also unable to string together dot balls or build any consistent pressure.

Root took the chance to look at two overs of Dan Lawrence's unconventional spin before the arrival of the new ball, but his first bowl in international cricket passed without incident. It took the fresh Kookaburra to shift the dial, with Curran and Mark Wood taking it ahead of Stuart Broad.

The pair immediately strung together two maidens, before Curran located just enough assistance to pick up the nick and end Thirimanne's stay after 251 deliveries. Mathews (30no) and Dinesh Chandimal (20no) put on another 32 before the interval, with the game settling straight back into its previous rhythm as the English attack struggled to assert itself.