South Africa captain Graeme Smith has urged his players to try to relax more in the field in an attempt to start taking catches instead of continually letting Australia off the hook.

The Proteas have spilled 11 catches this series, seven in the drawn first Test in Perth and another four in the second Test in Melbourne, which Australia won by 184 runs.

Of the four missed catches at the MCG, three were particularly costly and came from Australia's three century-makers.

In the first innings Ricky Ponting was dropped on 17 by Andre Nel (at mid-wicket) and made 117, and Mike Hussey was missed on 27 by Jacques Kallis (second slip) and reached 122.

Opener Matthew Hayden made 137 in the second innings after gaining a life on 27 when Nel missed a return chance off his own bowling.

Smith said the tourists had missed several chances to put Australia under pressure during the match and needed to be more ruthless on the field.

But ahead of next week's third Test at the SCG, Smith said the Proteas could not afford to fall for the trap of trying too hard and worrying more about dropping catches than taking them.

"It's almost like quicksand, the harder you try to get out of it, the more work you do, the deeper you sink," he said.

"Before the first Test we did slip work and a hell of a lot of catching and preparation on it because we knew it would be important.

"It's all about relaxing and allowing the catch to come, but the guys are more tense and more worried about dropping it than actually taking it and it's just about letting your natural ability take over."

Smith said South Africa was usually a good fielding side and thought signs of tension had crept in among some players when they played the world champions.

"We let ourselves down and we know that," he said.

"All the guys who put catches down are disappointed and they realise that it probably was a little bit costly.

"You've just got to pick yourself up and get back to work and get back on the job."

Brought to you by AAP © 2024 AAP