Kevin Pietersen has endured a tough series and his innings on Thursday was no different as the Hampshire batsman hit an easy catch to mid-on to fall for seven to leave England reeling.
"I'm sure he disappointed but he's been a rock in the dressing room," insisted Collingwood.
"We've always said he's one innings away (from a big score) and that could be the second innings."
Collingwood's knock included two sixes and his aggressive approach, in contrast to his defiant defensive innings in the drawn match in Cape Town, paid off.
"On a pitch like that it comes onto the bat really nice so, no matter what the situation, I think you have to back yourself to score runs. We've said from the start, we didn't come here to play for a draw," he said.
England changed their line-up for the first time in the series, with Sidebottom coming in to replace Graham Onions.
"Graham's disappointed but the captain and coach said we needed fresh legs," added Collingwood.
"Siddy's shown his accuracy and swing is going to be tough to play in these conditions."
Steyn, however, admitted he was surprised by the omission of Onions, who has taken eight wickets in the series.
Steyn swings South Africa into control
"He would have been a handful on this wicket - he gets very tight into the stumps and could have been very dangerous," said the South African paceman, who took 5-51 to complete his set of five-wicket hauls against major Test playing opponents.
"I'm not taking anything away from Ryan Sidebottom - he's also a very good bowler. But obviously Onions has troubled a lot of our batsmen throughout the series, and it's surprising to see he wasn't playing. It was a bit if a relief in a way."
Steyn also revealed he was aided by advice from former England spinner Jeremy Snape, who played 10 one-day internationals and one Twenty20 match between 2001-2007 and is now part of the South African backroom staff.
"Jeremy said at lunch I should take the ball away, away - then hold one across the seam and see if it goes straight.
"He said 'you should never under-estimate the straight ball'. So I said 'what about the inswinger?' - and he said 'if you can get it to go, fantastic' - so when I got the wicket I celebrated towards the dressing room."
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