Pietersen, who had a cortisone injection for a troublesome knee earlier this week, cracked 57 runs off 71 balls as he warmed up for his 100th Test starting in Brisbane on November 21.
Jonathan Trott (83) and skipper Alastair Cook (81) also spent valuable batting time in the middle, as England's top order fine-tuned for the first Test at the Gabba, reaching 302 for five at the close on the second day of the four-day tour match in Sydney.
At stumps, Joe Root was 26 not out and Jonny Bairstow was unbeaten on 11. England trailed by just two runs on the first innings after Steven Finn earlier staked his claim for the first Test fast bowling vacancy, finishing with five wickets for 103 to help dismiss the home side for 304 midway through the first session.
Pietersen looked scratchy early in his innings as he nicked a couple short and wide of the slips and hesitated on occasions when running between wickets with partner Cook.
But he appeared physically unencumbered during his 93-minute stay at the crease to further boost England's confidence ahead of the Ashes. He smashed seven fours and two sixes and almost seemed as if he was trying to get out when he skied legspinner James Muirhead (2-97) into the outfield.
"Kev seems fine, I haven't heard him complain about (his knee)," Trott said. "It's always nice to see him in full flow and being confident in warm-up
games. "But it doesn't really count now what the guys do, it's all about being ready and right for Brisbane on that first day."
Trott and Cook have both already posted first-class hundreds on tour, and the pair looked on track to do it again as they piled on an effortless 143-run stand after opener Michael Carberry (4) had fallen early.
But Trott edged one behind to give Josh Lalor (2-82) a second wicket, and keeper Peter Nevill a second diving catch. Cook departed a short time later, prodding at left-armer Nicholas Bills outside off-stump.
Ian Bell, coming off an outstanding Ashes series in England in July-August, was out edging Muirhead to Ben Rohrer at slip for 35 off 45 balls. The Invitational XI provided some bright moments in the field, but England proved far too strong for their bowlers.
However, Trott said his side have no reason to complain. "You're not going to face the Australian A side every week so you're going to face people who are State cricketers," Trott said.
"Today we were pretty happy with the standard of bowling we had. They were a lot better than what people have written about." England are searching for a third seamer to partner James Anderson and Stuart Broad at the Gabba, and Finn's improvement on day two may edge him ahead of Chris Tremlett, who is not playing in the Sydney game.
The Invitational side, resuming at 271 for five, lost Ryan Carters on the first ball of the day for 94, edging Broad to wicketkeeper Bairstow. Broad finished with four wickets for 37, an ideal lead-up to the opening Test for the fast bowler.