Sri Lanka's injury-hit cricketers took a pounding from South Africa's batsmen and bowlers on the third day of the first Test at SuperSport Park in Centurion on Monday.

Former captain Faf du Plessis led the batting assault, hitting 199 as South Africa took a commanding 225-run first innings lead.

Then fast bowler Lungi Ngidi struck twice at the start of Sri Lanka's second innings to leave the tourists struggling on 65 for two, still 160 runs behind, on a pitch of increasingly unpredictable bounce.

Sri Lanka's injury woes continued and at one stage three of their five regular bowlers were off the field as South Africa amassed a first innings total of 621.

Kasun Rajitha, who suffered a groin injury at the start of the innings on Sunday, did not take the field again and fellow fast bowler Lahiru Kumara suffered a similar injury soon after lunch after bowling a single ball in a new spell. He also did not return.

Debutant leg-spinner Wanindu Hasaranga was off the field for part of the afternoon after falling on the ball trying to make a diving save on the boundary. But he returned to finish with four wickets, albeit at the high cost of 171 runs.

Sri Lanka will face an uphill battle to avoid defeat, with batsman Dhananjaya de Silva not expected to bat after being ruled out of the series with a torn thigh muscle.

At one stage, Sri Lanka had four substitutes on the field, while captain Dimuth Karunaratne and Kusal Mendis were called into action as emergency bowlers.

Du Plessis misses double century 

Du Plessis and the other South African batsmen took advantage with a free-scoring display. Du Plessis made his highest Test and first-class score and appeared to be cruising to a double century before he tried to loft Hasaranga over his head and hit a simple catch to Karunaratne at mid-on.

Du Plessis shared partnerships of 179 for the fifth wicket with Temba Bavuma (71) and 133 for the seventh wicket with Keshav Maharaj, who made a Test-best 73.

Bavuma's innings ended unusually when he flashed at a ball from the medium-paced Dasun Shanaka and immediately started walking back to the dressing room as the ball carried to wicketkeeper Niroshan Dickwella. Umpire Marais Erasmus was not called upon to make a decision.

Replays showed there had been no contact between bat and ball, with no spike showing on the ultra-edge. A clear gap was visible as the ball went past the bat.

The boundary which brought up Du Plessis' century also made the former captain the ninth South African to reach 4000 Test runs. His hundred was scored off 151 balls and included 15 fours.

Ngidi bowled the left-handed Karunaratne in the third over of the second innings with a ball delivered from around the wicket which kept low and crashed into the off stump. He followed up by having Mendis caught at first slip.

Kusal Perera and first innings top-scorer Dinesh Chandimal saw Sri Lanka through to the close, scoring at close to a run a ball as South Africa set attacking fields.