Rangana Herath took six wickets as Sri Lanka completed a 199-run win over South Africa to sweep the two-test series with a day to spare.

The veteran spinner snared 6-98, including the vital wicket that broke up South Africa's 123-run sixth-wicket stand just before lunch on Monday.

Theunis de Bruyn (101) posted a maiden test century and was involved in the partnership with Temba Bavuma (63) that delayed the inevitable after South Africa was set an improbable target of 490 to level the series. The Proteas were eventually dismissed for 290.

"When we play at home we know that spin will play a part and we have some of the best spinners in the world. We played like a team and very pleased with everyone's contributions. We knew that they will struggle when the ball turns," Sri Lanka stand-in skipper Suranga Lakmal told journalists.

Sri Lanka opener Dimuth Karunaratne, who posted twin fifties in the game and accumulated 356 runs in the series at an average of 115, was named Man of the Match and Player of the Series.

"You have to know what your strengths are when you are playing spin. Theunis de Bruyn for example showed you how to play on wickets that turn. I am sure he would have struggled earlier on in the innings, but once you spend some time in the middle it gets easier. He was sweeping well. Used his feet well and that's the best way to play spin," Karunaratne said.

South Africa resumed the day on 139 for five and De Bruyn quickly posted his side's first half-century of the series and Bavuma soon joined him.

Just as it appeared the Proteas would bat through a session without losing a wicket Herath struck nine minutes before lunch when Niroshan Dickwella completed a good low catch to dismiss Bavuma and Quinton De Kock followed two balls before the break.

De Bruyn scored his century when play resumed but fell to Herath four balls later. He batted for 12 minutes short of five hours, facing 232 deliveries and hitting 12 boundaries.

Sri Lanka then completed the win when Dale Steyn was caught at long-on by Danushka Gunathilaka for Herath's final wicket.

"Whenever a team tours the subcontinent - whether it's Australia or England or us - there's always a question mark on how you play spin. It's a world issue that we're trying to get better at. I don't think we play spin badly, but if you compare yourself to the subcontinent batters, then they're obviously a step above us in that regard," South African skipper Francois Du Plessis said.

Sri Lanka won the first Test in Galle by 278 runs.

The teams begin a five-match ODI series Sunday in Dambulla, which will be followed by one T-20 international.