Johnson ripped apart England's top order in the first innings with a match-turning six wicket haul that propelled Australia to an emphatic 267-run victory that leveled the five-match series at 1-1.
"(It) Definitely took us by surprise, for sure, but he bowled well, bowled really, really well, he bowled a really good game of cricket, Pietersen, who was trapped lbw for a duck by Johnson in Perth, told reporters.
"Obviously we're going to prepare ourselves for that swinging ball. We knew he was going to swing it, but we didn't think he was going to swing it that much."
Johnson said he had enjoyed taking Pietersen's wicket and described him as a 'smart-arse' after the South Africa-born batsman had asked him teasingly for his phone number so they could be 'best mates'.
Johnson declined to give it, and Pietersen, who remains firm friends with Australia's retired leg spinner Shane Warne, confirmed the players were far from being on good terms.
"I don't have a relationship with Mitchell Johnson," Pietersen said, repeating himself when pushed to clarify.
Australia's bowlers credited their improved performance at Perth in part to a renewed aggression that saw them exchange heated words with a number of English batsmen amid peppering them with volleys of furious short-pitched bowling.
Pietersen denied England had been unsettled by any verbal attacks and said he had heard worse when facing the likes of Warne and retired paceman Glenn McGrath during England's last Ashes tour four years ago.
"I haven't seen or heard anything different to anything that's happened in the first two Test matches let alone last year in England," he said.
"There's not really any big chirpers or big sledgers.
"It's just England versus Australia, it's an Ashes series. Blokes get a bit of red mist occasionally.
"It's historic, it's huge, but there's nothing that's been overboard and if things go overboard, match referees deal with stuff like that."
Pietersen also shrugged off controversy over the choice of pitch at the Melbourne Cricket Ground where the fourth Test gets underway on Sunday.
Pitches for the MCG are dropped into the oval and English media have cried foul that the head groundsman would choose a grassier wicket more suited to Australia's quicks rather than a drier track that might favor England and particularly, spinner Graeme Swann.
"Of course, they're going to do it, they just had success in Perth with a bouncy wicket, but we've had success around the world with bouncy wickets," Pietersen said, attributing England's loss to their disastrous first innings collapse, rather than the pitch.
"We lost that Test match in half an hour, (with) five (wickets) for 20, that's where we lost that Test match."
