Graeme Smith says his South Africa team will be motivated by toppling Australia from their world championship throne when they play West Indies in the fourth Test starting on Friday.

South Africa have an unassailable 2-0 lead in the four-match series, and another win would put them within sight of the Australians at the top of the Test rankings.

"We're focused on beating the West Indies at Centurion because we know that winning the series 3-0 will take us a few points closer to Australia," Smith told reporters on Thursday.

"It makes no difference to us that the series has been decided, we're determined to do well at Centurion."

Smith rates his team's batting ability as similar to Australia's.

"I think we can match the Aussies as a batting unit," Smith said. "Jacques Kallis and Herschelle Gibbs have been brilliant."

Kallis has been the most prolific batsman in the series, scoring 582 runs at an average of 145.50 with three centuries.

Gibbs has scored two centuries among his 383 runs, which he has accumulated at an average of 95.75.

Smith said his team would look to improve their application at the crease in the fourth Test, an area of concern when they lost three wickets late on the first day of the drawn third match in Cape Town.

"Careless shotmaking got us into a bit of trouble on the first day at Newlands and we want to improve on that," Smith said.

Left-arm wrist spinner Paul Adams was retained in the squad despite an ineffective performance in Cape Town where he failed to take a wicket and conceded 173 runs from 41 overs.

Smith hinted that Adams, the only specialist spinner in the squad of 13, would get another chance in Centurion.

"It's difficult to go into a Test match without a spinner, it's dangerous and risky," Smith said.