The 34-year-old surpassed his previous County Championship best of 254 in a mammoth innings for Surrey against Leicestershire at The Oval, on the eve of Andrew Strauss’ first public address as England’s new cricket director.
Pietersen notched his first County Championship double century since July 2012 – then set a new personal first-class record, beating that 254 not out for Nottinghamshire against Middlesex in August 2002.
The free-scoring star ended the second day of this Division Two match with a maiden triple century, unbeaten on 326 with 34 fours and 14 sixes from 373 balls.
Surrey closed day two on 528 for nine, leading Leicestershire by 236 runs.
Former Test captain Strauss will confront Pietersen’s situation at Lord’s on Tuesday, after stepping into a newly-created figurehead role at the England and Wales Cricket Board.
England will on Thursday finalise their squad to face New Zealand at Lord’s in the first Investec Test next week, with Pietersen’s near-imperious knock at The Oval forcing Strauss to review the South Africa-born outcast’s position.