Seven bowling innings, 21 Test wickets, and on a day in which the left-arm spinners went missing in stretches, an outstanding 6 for 70, which brings the average down to 23.52. If you'd followed Ramesh Mendis at first-class level or in the Sri Lanka A side, you might have thought - oh, here's a decent batting allrounder who can do the job with the ball.

But Sri Lanka has a knack of finding spinners in unusual places (though, to be fair it must also be said that Sri Lanka tracks have a knack of making hotshot spinners out of almost anyone - Kraigg Brathwaite has a six-wicket haul at the P Sara Oval). And on Wednesday, Mendis was diligent, where Lasith Embuldeniya and Praveen Jayawickrama had been loose. Where the lefties missed their lengths, letting the batters rock back to crash the ball square too often, Mendis worked the pitch like an accountant with a set of tax forms - his work conscientious, repetitive, light on the glam. Just like this answer to the question, "what is it that brought you success, on arguably the best day of his career so far?"

'The pitch wasn't turning as much as we thought it would, from even the afternoon yesterday," Mendis said. "So we got together with the coaches and the plan was to bowl a lot of dot balls, and bowl just to one spot. We didn't have a lot of runs to defend. I just put the ball in the right place."

If that's a workaday answer to match a workaday style, the impact of his big spell certainly wasn't. West Indies were only 24 runs behind at that stage, and had six first-innings wickets in hand. They bat deep, Joshua da Silva coming in at No. 8. How big was the lead going to be? Triple-figures? In Galle, those leads don't get ate up in the back end of a Test. Sri Lanka had denied West Indies a win on the island for almost 30 years. Brian Lara, Courtney Walsh, Curtly Ambrose, Richie Richardson - they've all been here, and not all the Sri Lanka sides they met were strong. If Sri Lanka were going to be decked on their home turf, was it really going to be by this West Indies team?

But Mendis had been putting in the work. Either side of lunch, he bowled 20 overs unchanged with a barely-responsive old ball, giving only 35 runs away. Just after drinks in the second session, he switched ends, took the second new ball. And just as Veerasammy Permaul and Jomel Warrican had found on day two, if you can blow one batter down, at Galle you could spin yourself to a tornado of wickets. Roston Chase was first to go, the ball spitting more than he expected with its hard new seam, the catch flying to leg slip. Hope went two Mendis overs later, hit in front, clipping leg. And then, two in two (which Mendis had made happen in the first Test of this series as well); Jason Holder hit in front, the doughty da Silva bowled by one that didn't turn.

Four wickets in the space of 17 runs for West Indies; four in the space of 19 balls for Mendis - look, you get it, this spell was not game-turning necessarily, because we don't know where we wind up on Friday, but it was, at the very least a significant veering away from the set course.

If you're looking for a "the coming of Sri Lanka's next spin hope" type conclusion, we're too smart, been burned before, don't understand the selectors, and so we don't do that here. (Remember that other Mendis?) But, okay, here are some bright nuggets. Athough West Indies have seven right-handers in their top eight, Mendis, who turns the ball into them, has still been Sri Lanka's best spinner of the series (all six of his victims in this innings were right-handers). With a tour of India, and home Test series against Australia and Pakistan coming up next year, Mendis is collecting for himself a happy mound of confidence.

Plus, he's got a first-class batting average of more than 40, you know, so it's possible we have not seen the best of his batting yet. By his own admission, he's been asked to play more as a bowling allrounder in the national side, and so far, in his four Tests, that is exactly what he has seemed.

But Sri Lanka have three young spinners on the go now, and on Wednesday, when two of them were a distance from their best, the offie held the fort with a lengthy old-ball spell, and when the new one was thrown to him, broke through big.

Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. @afidelf