'Tough to prepare for Johnson'

Pretoria - The South Africans knew what was coming, they just didn't know what to do about it.

SA v Oz - Day 3 as it happened

Mitchell Johnson's destructive form was forecast after his 37 wickets in five matches led Australia's Ashes demolition of England.

Yet, South Africa coach Russell Domingo said there's nothing a team can do to prepare for the searing pace and aggression the quickest bowler in the world is generating.

Not even the top-ranked team in Tests.

Johnson took 7-68 on Friday with his uncomplicated bowling - fast and short-pitched - to rock the South Africans and put Australia firmly on course for an opening-Test victory at SuperSport Park, a ground where South Africa's quicks normally bully the opposition.

"Look, our preparation has been as good as it's ever been, but there's nothing that can prepare you for that kind of intensity," Domingo said.

"You're never going to be able to replicate that in nets."

Domingo realised South Africa was encountering the left-arm quick "on a hot streak."

And there was no secret, nothing subtle about Johnson's intentions.

"My plan was really to bang the wicket hard and it came off," Johnson said after his first four wickets on the second day, which included an opening spell of 3-10 in four overs.

The bowling by Australia's left-arm weapon was blisteringly fast in that first spell of the series, so quick that almost all of South Africa's top order struggled badly - as most of England's top order did Down Under.

The spiteful delivery to remove Faf du Plessis was clocked at around 150 kph and drew a couple of tweets from England's Kevin Pietersen.

Most of the world's quickest quicks operate in the lower 140s.

"There is a HUGE difference when facing someone at 140kmh compared to 150kmh," Pietersen tweeted.

"When you facing someone as quick as Mitchell, your instinct occasionally makes you do things you shouldn't. PACE causes indecision!"

Armed with that raw pace, Johnson also has had one of the world's quicker pitches to attack on at SuperSport, where even he was surprised by the bounce and pace he got.

Describing the brute that sent Graeme Smith back, Johnson said: "The ball did take off and I'll keep using it."

There's still no hiding what's coming from Johnson for the rest of the series. But what can you do about it?

*NOTE: An earlier headline referred to Mitchell Johnson as being "unplayable" which has subsequently been changed to the current headline: 'Tough to prepare for Johnson'