Mitchell Johnson is confident he will take on South Africa in good form after collecting five wickets to help Western Australia to victory in their Sheffield Shield match against Tasmania on Friday. Importantly, Johnson said he was finding some swing during the four-day game at the WACA, after he struggled to have a major impact during the recent Test series in Sri Lanka.

Johnson has had a difficult 12 months, having collected only 21 Test wickets at 41.28 since the start of the Ashes. However, South Africa was the scene of one of Johnson's most successful periods in international cricket in early 2009, when he moved the ball in the air and bowled with aggression to help Australia to a 2-1 Test series win.

"I was happy with the rhythm throughout this [Shield] game," Johnson told reporters in Perth after the match. "The ball swung out there for me a fair bit. I'm just really in a good place at the moment. I feel in good nick. The wickets [in South Africa] are probably going to be a little similar [to the WACA], with that early-on seam. So I'm looking forward to that again. I'm confident at the moment."

He will join Australia's squad in South Africa for the three one-day internationals, which begin on Wednesday in Centurion, and the two Tests that follow. Although the Test squad has not yet been named, Johnson is expected to be a key member of the attack, along with Ryan Harris and Trent Copeland, who both bowled well in Sri Lanka.

Johnson picked up 5 for 69 in the second innings of the Shield game, including the key wicket of Tasmania's captain George Bailey, who had made a century and was threatening to take the game away from Western Australia. It was a fine turnaround for Johnson after he rolled his ankle on the first day of the match.

"I've done it a few times now. I thought I did it worse this time," Johnson said of the injury. "But it turned out fine. I've just got to keep strapping it and get a bit of strength into it."

Johnson flew out of Perth on Friday night to join the Australians, who won the first Twenty20 in Cape Town on Thursday. The second T20 will be played at the Wanderers in Johannesburg on Sunday.