The batsman blasted his way to a near run-a-ball ton for Surrey in their LV= County Championship match against Yorkshire at Headingley.
Pietersen's selection in next month's Trent Bridge opener had been placed under some uncertainty after he took longer than expected to recover from a knee injury which caused him to fly home from England's tour of New Zealand in February.
Pietersen was in fine fettle 16 days before the Ashes begins
The 32-year-old reached his century from just 106 balls - and went on to hit 17 fours and seven sixes.
And by the way - after fielding for 136 overs, my knee feels top drawer!! All smiles this Sunday!!
— Kevin Pietersen (@KP24) June 23, 2013
Provided he suffers no setbacks, Pietersen is due to make his England return in Thursday's second Twenty20 international against New Zealand at The Oval.