Kumar Sangakkara and Mahela Jayawardene scored undefeated half-centuries to give Sri Lanka the initiative after South Africa were dismissed for 169 on the first day of the opening test on Thursday.
The hosts wobbled early on in their reply, losing both openers Sanath Jayasuriya and Upul Tharanga cheaply, but Sangakkara and Jayawardene then scored freely during an unbroken 114-run partnership that left Sri Lanka on 128 for two at the close.
Sangakkara, given a double let-off in the eighth over when he was dropped in the gully and then bowled off a no ball, led the assault with 59 from 66 balls that included 10 stylish boundaries.
Jayawardene, Sri Lanka's stand-in captain, provided solid support with 55 from 76 balls as the scoring rate climbed above five runs per over, pushing South Africa on to the defensive.
South Africa failed to capitalise after winning the toss, collapsing dramatically as wickets tumbled during the two-hour afternoon session.
The collapse was inspired by fast bowler Dilhara Fernando and spinner Muttiah Muralitharan who claimed four wickets apiece.
Bowling full and straight on a pitch offering some early seam movement, Fernando dismissed openers Andrew Hall (17) and Herschelle Gibbs (19) before lunch and then helped clean up the tail in the afternoon to finish with four for 49.
Muralitharan, bowling with his left-hand heavily strapped after splitting his webbing around his thumb, made deep inroads into the middle order and then finished off the innings to claim 4-41.
AB de Villiers provided the only resistance with an aggressive 65 from 72 balls that included eight boundaries before he was the last man out as he tried to thrash late boundaries.
South Africa's troubles began early as Hall dragged a full-length delivery onto his stumps and Gibbs was defeated by a ball that nipped back off the pitch to clip his off stump.
The tourists then became becalmed against Muralitharan who started with four consecutive maidens.
However, left-hander Jacques Rudolph, called up after injuries to skipper Graeme Smith (ankle) and Jacques Kallis (elbow), increased the tempo towards the end of the session, hitting five boundaries.
But Farveez Maharoof snared a brace of wickets straight after lunch as first Rudolph (29) and then stand-in captain Ashwell Prince (1) edged to Prasanna Jayawardene behind the stumps.
Hashim Amla added 32 with de Villiers before he was deceived by Muralitharan's doosra and stumped.
The 33-year-old off spinner then quickly claimed the scalps of Mark Boucher (4) and Nicky Boje (5) before Fernando was recalled into the attack to dismiss tailenders Andrew Nel and Dale Steyn.
Sri Lanka's reply started badly as pace bowler Dale Steyn trapped Jayasuriya lbw for four and Tharanga was caught behind for seven.
But Jayawardene and Sangakkara, riding their luck early on, saw-off the new ball and batted comfortably until the close.
Scorecard
South Africa 1st innings
H. Gibbs b D. Fernando 19
A. Hall b D. Fernando 17
J. Rudolph c P. Jayawardene b Maharoof 29
H. Amla st P. Jayawardene b Muralitharan 19
A. Prince c P. Jayawardene b Maharoof 1
A. de Villiers c Kapugedera b Muralitharan 65
M. Boucher c Jayasuriya b Muralitharan 4
N. Boje lbw b Muralitharan 5
A. Nel lbw b D. Fernando 0
D. Steyn b D. Fernando 0
M. Ntini not out 0
Extras (b-4 lb-6) 10
Total (all out, 50.2 overs) 169
Fall of wickets: 1-32 2-45 3-78 4-80 5-112 6-128 7-148 8-151 9-151 10-169
Bowling: L. Malinga 10 - 2 - 38 - 0, F. Maharoof 9 - 1 - 32 - 2, D. Fernando 13 - 2 - 48 - 4, M. Muralitharan 18.2 - 6 - 41 - 4
Sri Lanka 1st innings
U. Tharanga c Boucher b Steyn 7
S. Jayasuriya lbw b Steyn 4
K. Sangakkara not out 59
M. Jayawardene not out 55
Extras (nb-2 w-1) 3
Total (for 2 wickets, 26 overs) 128
Fall of wickets: 1-6 2-14
To bat: T. Dilshan, C. Kapugedera, P. Jayawardene, F. Maharoof, L. Malinga, D. Fernando, M. Muralitharan
Bowling: M. Ntini 7 - 3 - 22 - 0, D. Steyn 6 - 0 - 30 - 2 (nb-2 w-1), A. Nel 6 - 0 - 32 - 0, A. Hall 5 - 0 - 34 - 0, N. Boje 2 - 0 - 10 - 0
