COLOMBO: Shane Watson shone with bat and ball for the fourth match in a row as Australia stepped closer to the World Twenty20 semi-finals with an eight-wicket win over South Africa on Sunday.

Watson claimed 2-29 and then smashed 70 off 47 balls as Australia restricted the Proteas to 146-5 and then surpassed the total in the 18th over to record their second successive win in group two of the Super Eights.

South Africa, who suffered their second loss, will be knocked out of the tournament if Pakistan beat India in the second match of the double-header later on Sunday.

That result would also see former champions India exit from the competition, leaving Australia and Pakistan as the two semi-finalists from the group even before Tuesday's last round of matches.

Australia lost David Warner in the fourth over, bowled by Morne Morkel, before Watson and Mike Hussey added 99 in 64 balls for the second wicket.

Watson, who was adjudged man of the match for the fourth consecutive game, hit eight boundaries and two sixes before being caught in the deep off Robin Peterson.

Mike Hussey remained unbeaten on 45, while Cameron White made 21 not out, including the winning six off Johan Botha over the mid-wicket boundary.

Watson and left-arm spinner Xavier Doherty set up the emphatic win by sharing the five wickets after South Africa were sent in to bat at the Premadasa stadium.

JP Duminy's 30 was the best score by a top-order batsman as South Africa slipped to 86-5, before Farhaan Behardien and Peterson added 60 from 35 balls for the unbroken sixth wicket.

Behardien made 31 not out and Peterson returned unbeaten on a brisk 32 off 19 balls, the pair taking 28 runs in the final two overs.

Doherty, opening the bowling after replacing seamer Daniel Christian for the match, removed Richard Levi with the third delivery and sent back Jacques Kallis in his second over.

It became 33-3 in the sixth over when Watson struck fifth ball as Hashim Amla edged a leg-side catch to wicket-keeper Matthew Wade after making 17.

Doherty, returning for his second spell in the 11th over, had Duminy stumped and Watson dismissed skipper AB de Villiers to reduce the Proteas to 86-5 in the 15th over.

Australia: George Bailey (capt), David Warner, Shane Watson, Matthew Wade, Michael Hussey, Cameron White, Glenn Maxwell, Brad Hogg, Xavier Doherty, Mitchell Starc, Pat Cummins.

South Africa: AB de Villiers (capt), Hashim Amla, Farhaan Behardien, Johan Botha, JP Duminy, Jacques Kallis, Richard Levi, Morne Morkel, Wayne Parnell, Robin Peterson, Dale Steyn.

Umpires: Ian Gould (ENG) and Kumar Dharmasena (SRI) TV umpire: Richard Kettleborough (ENG) Match referee: Jeff Crowe (NZL)