Captains Graeme Smith and Michael Clarke will be under greater than usual pressure when South Africa and Australia clash in the series-deciding third Test from Saturday.

Apart from the normal challenge of trying to win a showdown at Newlands between two of cricket´s top teams, both skippers will be seeking to end a run of poor personal form with the bat.

And both will be facing bowlers who have been a nemesis during their careers.Smith has had scores of 10, 4, 9 and 14 in the first two Tests, while Clarke has made 23, 17 not out, 19 and 1.

Smith has been out three times to left-arm fast bowler Mitchell Johnson, who has now dismissed him eight times in 10 Tests.

No bowler has claimed his wicket more often in Tests, although Chris Martin of New Zealand also got him out eight times in 11 matches.

Clarke has fallen twice to Dale Steyn, taking his number of dismissals against South Africa´s fast bowling kingpin to nine in 13 Tests, equal with Englishmen James Anderson (23 Tests) and Stuart Broad (17 Tests).

Both captains have rejected concerns about their form.Smith points out that he scored a double century against Pakistan five Tests ago and that he has had success as well as failures against Johnson.

"I´ve faced Mitchell a lot of times -- times where he´s had the better of me and times where I have had the better of him," he said before South Africa squared the series by winning the second Test in Port Elizabeth.

After the double century against Pakistan, Smith made only 47 runs in four one-day innings against Pakistan but had scores of 68, 44, 47 and 27 not out in a two-Test series against India.

Clarke´s highest score in 11 Test innings since he made 148 against England in the second Ashes Test in Adelaide has been 24. In four one-day innings against England he had a best of 43.

Asked about his recent form after the second Test, Clarke said: "Obviously I´d like to score a hundred every time I bat.

Clarke´s "great times" were exceptional. In the 2012 calendar year, he hit 1,595 Test runs at an average of 106.33, with a triple century and three double centuries. Two of the double centuries were in a home series against South Africa.

The Australian captain, who before his second innings in Port Elizabeth said he felt in "great nick", hoped he wouldn´t have to answer questions about his form in future press conferences. "I´m due," he said.

Both captains have had success at Newlands. The last time they came up against each other in Cape Town, in November 2011, Clarke hit 151 in an Australian first innings total of 284 before being dismissed for two when Australia were routed for 47 in the second innings.

Smith top-scored with 37 in South Africa´s first innings of 96, then guided his side to an eight-wicket win with an unbeaten 101. (AFP)