The England batsman blasted nine sixes and six fours on his way to an unbeaten 103 from 64 balls as the hosts chased down their 158 victory target with five deliveries to spare.
He was dropped thrice along the way, including once when he was on six, with his performance coming after most of his team-mates flopped with the bat, although Yogesh Nagar provided a handy unbeaten 23 off 15 that enabled Delhi to get home.
Shahbaz Nadeem (3-16) and Morne Morkel (3-23) had earlier shared six wickets when the visitors were restricted to 157 for eight.
Morkel’s performance took him to 12 wickets for the season and enabled him to take hold of the purple cap, worn by the competition’s leading wicket-taker.
Parthiv Patel struck 45 off 27 and Shikhar Dhawan hit 44 off 29 for the 2009 IPL champions after they had won the toss and batted first.
The two shared a 71-run partnership together, but once they fell the lower order failed to deliver as Deccan remained the only winless side in the competition after four games.
In reply, Veer Pratap Singh dealt Delhi a blow in the first over by removing Naman Ojha (one), caught by JP Duminy at point.
The hosts were then dealt two massive blows one after the other as Dale Steyn drew Virender Sehwag (seven) into chasing a slightly wide ball with a thick edge caught well by Dan Christian at slip.
Seven deliveries later Mahela Jayawardene (six) came down the track to the Australian and miscued to Kumar Sangakkara at mid-off.
Delhi were in a spot of bother at that stage on 23 for three, but Pietersen reacted by blasting Amit Mishra’s first over for 17, including a back-foot cut for six, with the costly six deliveries taking the home side past 50.
That was in the eighth over of the chase and two overs later, Dhawan brilliantly through down the stumps from cover point to get rid of Ross Taylor (13).
But Pietersen kept going, and after raising his third IPL career 50 from 42 balls with a single at the start of the 13th over, he then lifted the South African for three successive sixes.
Duminy should have had a measure of revenge with the final ball of the over but dropped a return catch.
Steyn returned to the attack in the 15th over and got Irfan Pathan (five), but it was not the right man Deccan had dismissed with Pietersen finding a good foil in Nagar.
With 37 required from the last 24 balls, the crucial moment came when the 17th over went for 15.
Pietersen brought up his first ever hundred with a six to record his best ever score, which comfortably surpassed his 79 against Zimbabwe in 2007.