Pietersen's only match on English soil before next week's first Test against West Indies had looked to be turning sour when he managed just 11 as Surrey were skittled for 113.
But the right-hander's brazen 69, after Surrey were asked to follow on, inspired a turnaround of sorts as the visitors' reached the close on day three at 216 for four. That constituted a lead of 44 runs that had looked unlikely when four of Surrey's top six made ducks in their disastrous first innings.
Only South African opener Jacques Rudolph's 68 - before he was last man out - saved them from complete embarrassment. Surrey's position got even worse, with Pietersen called to the crease after Mark Ramprakash was dismissed for a pair at 11 for two.
But from there Pietersen took charge to show he was ready to face the Windies at Lord's, a week after arriving back from the Indian Premier League, striking 10 fours and a six in his 85-ball 69. Pietersen's knock was a stand-out performance in a round of matches that England's batsmen have otherwise struggled.
Middlesex staged a recovery against
Ollie Rayner led the way with an unbeaten 143, with England pair Stuart Broad (one for 73) and Graeme Swann (two for 55) having to take a back seat, before Middlesex declared on 300 for nine - 123 runs in arrears.
The declaration proved inspired as Nottinghamshire slumped to 22 for three by the close - the impressive Rayner claiming two while Steven Finn followed his four first-innings wickets by grabbing the other.
Rain continued to play havoc around the grounds with
Tim Bresnan pushed his England claims with five for 81 as
The hosts declared at 351 for nine, after accelerating via some declaration bowling, and when Yorkshire forfeited their first innings, Worcestershire curiously batted again to post a victory target of 400.
Yorkshire were 30 for one in pursuit, with Joe Sayers (one) falling to Will Gidman.
At Chelmsford, Cook failed to reach double figures for the third time in as many innings for
Darren Stevens (119) and Geraint Jones (88) had earlier contributed most of
Ravi Bopara finished the day heading to hospital for a scan, after being forced off after bowling a solitary over, but Essex maintained it was a precautionary move only.
Jimmy Adams made 122, while Bilal Shafayat hit 93 on his
After the opening two days were washed out, and a result unlikely, both sides set about at least retrieving some bonus points from the match.
Kyle Coetzer hit 120 as