Eventually, Pietersen admitted on Wednesday: "I did send what you might call provocative texts to my close friends in the South African team.
"The texts were meant as banter between close friends. I need to rein myself in sometimes. I apologise to Straussy and the team for the inappropriate remarks at the press conference and for the texts.
"I truly didn't mean to cause upset or tension particularly with important games at stake."
Throughout his tenure as captain, Strauss, for whom Thursday's match represents his 100th Test and 50th as captain, has tried to keep Pietersen, his predecessor as skipper, on board.
So it was no surprise to hear Strauss say on Wednesday that he felt "let down" by Pietersen.
"I feel a little bit let down by Kevin, if I'm honest," said Strauss.
"But this isn't an issue between me and Kevin. It's a broader issue than that and it's very important that I act in the best interests of England cricket team.
"It's not a personal thing. I've always got on very well with Kevin, which is why some of the stuff has been quite surprising to me."
Strauss acknowledged Pietersen's apology by saying: "It's a step forward, it's a step in the right direction. But this issue hasn't just been about the text messages.
"There's been a bit more of a broader issue about trust and mutual respect, and that issue I'm very keen to resolve.
"If we're going to resolve those issues we need to do it face to face, away from the media spotlight and away from PR companies and press releases.
"That's not helping any of us at this stage."
Strauss no longer plays Twenty20 cricket and Pietersen will also have to mend some fences with England Twenty20 captain Stuart Broad.
The allrounder said he'd no role in a parody Twitter account for Pietersen. The account - KP Genius - was set up by a friend of Broad, Richard Bailey, and had been thought to have contributed to the strained relations Pietersen felt within the England dressing room amid suggestions some of his team-mates were involved.
But Broad insisted: "I would like to confirm that I had no involvement in this whatsoever.
"As has been widely reported Mr Bailey is a friend of mine, but we had no conversations regarding this issue at all and I am pleased that he has now decided to close the parody account down."
England batsman Kevin Pietersen will discover by Saturday if his apology for sending "provocative texts" to South African players has come in time to salvage his hopes of playing in the World Twenty20.
Throughout months of escalating tension with the England and Wales Cricket Board (ECB) hierarchy, Pietersen has always expressed the wish to help England defend the trophy they won in the Caribbean two years ago when he was named man of the tournament.
Saturday is the International Cricket Council deadline for teams to name their final squads for this year's edition, in Sri Lanka starting in September.
Pietersen's apology, issued Wednesday, came too late to save his place in the team for the third and final Test against his native South Africa at Lord's starting on Thursday.
Last weekend England dramatically dropped Pietersen from their squad for Lord's, even though he scored a brilliant 149 in the drawn second Test in Leeds.
Pietersen was axed for failing to reveal the contents of those text messages, some of which were said to contain criticisms of England captain Andrew Strauss.