South African captain Graeme Smith has announced he will retire at the end of his side’s series-deciding Test against Australia in Cape Town.

Smith, 33, broke the news to teammates after Monday’s third day of the Third Test at Newlands.

“This has been the most difficult decision I have ever had to make in my life,” said the 116-Test veteran.

“It’s a decision that I have been considering since my ankle surgery in April last year.

“I have a young family to consider, and I felt that retiring at Newlands would be the best way to end it because I have called this place home since I was 18 years old.”

Smith has scored 9257 runs at an average of 48.72 during his 12-year Test career.

Australia held a 234-run lead over the Proteas at stumps on day three of the Test, with all 10 wickets in hand and David Warner already 25 from 17 balls.

South Africa have much work to do if they’re to avoid a defeat that would result in a first Test series loss since March, 2009 – also against Australia at home.

Clarke ended the visitors’ first innings at 7-494 before the start of play on Monday, and the timing of his next declaration will help decide the series.

Faf du Plessis, who top-scored with 67 in his side’s first innings of 287, famously batted for almost eight hours to secure a draw on Test debut 16 months ago in Adelaide.

Du Plessis also soaked up 309 balls in another recent dramatic draw, against India in Johannesburg three months ago.

The Proteas were chasing targets of 430 and 458 in those respective matches, and survived approximately four and a half sessions.

Du Plessis expected his side’s dogged digs to be at the forefront of Clarke’s mind at Newlands on Tuesday, when Australia will look for quick runs to be in a position to declare at lunch.

“He will go more on the aggressive side,” du Plessis said of Clarke’s declaration.

“We have done it a few times … we will still be comfortable to bat out time.

“It’s a tricky one for them … if you bat for too long you take time out of the game and if you bat for a short period of time, you give us a chance.”

Mitchell Johnson and Ryan Harris bowled magnificently as the world’s No.1 Test side fluffed their lines after Clarke’s masterful knock of 161 not out.

Johnson (4-42 from 19 overs) dismissed Alviro Petersen (53), in-form AB de Villiers (14), du Plessis and hamstrung Dale Steyn (28) to overtake Jason Gillespie and rise to sixth on Australia’s all-time Test wicker-takers.

The left-armer suggested the final 10 wickets wouldn’t come easy.

“It’s an Adelaide type of wicket … they did a pretty good job keeping us out (there),” Johnson said.

“I don’t know how much time we need.

“Five sessions would be really nice, but it depends how many runs we can get (before lunch).”

James Pattinson broke down in the first innings of the 2012 Test in Adelaide and Shane Watson wasn’t in the XI.

This time Australia’s attack is both fitter and better.

“Once we saw the ball reversing it was a different game out there, so we’re quite confident (of winning) if we can put some runs up,” Johnson said.

Harris (3-63 from 22 overs) returned to form with devastating effect, swinging the ball well to collect the scalps of second-Test centurions Hashim Amla (38) and JP Duminy (four), and Graeme Smith (five).

Steyn will undergo a fitness test to determine if he can bowl in the match.