South Africa boosted their chances of qualifying for their first World Test Championship final after a 109-run victory over Sri Lanka in the second and final Test as they wrapped up a 2-0 series sweep at St George's Park in Gqeberha.

Chasing 348, Sri Lanka needed 143 runs with five wickets in hand on the fifth morning of the second Test, with overnight batters Kamindu Mendis (46) and Dhananjaya de Silva (50) at the crease.

But Mendis edged spinner Keshav Maharaj (5-76) to Aiden Markram at slip to bring an end to their 97-run partnership before Kagiso Rabada (2-63) caught the outside edge of De Silva's bat, the Proteas removing both set batters within the first half hour of play.

Marco Jansen (1-54) then combined with Maharaj to dismiss Sri Lanka's tailenders with Prabath Jayasuriya (9), Vishwa Fernando (5), and Lahiru Kumara (1) all out in single figures as the visitors were bowled out for 238.

Maharaj took three of the five wickets on the final morning to claim his 11th career five-wicket haul.

South Africa now move to the top of the World Test Championship standings ahead of Australia and India, with two more home Tests to come against Pakistan starting on December 26, while defeat for Sri Lanka means their hopes for the Lord's final have all-but ended.

"This Test for a lot of the guys was a proper Test. It's rare that you get to play all five days and rare the game swings both sides," said South Africa captain Temba Bavuma.

"Credit to Sri Lanka for the way they went about their business. They asked the right questions, they made us work hard for the win.

"The World Test Championship table looks good, we still have two games to go. I don't know what the math looks like but we want to continue what we're doing, enjoy the victory, and in a couple of weeks, start speaking about Pakistan."