At the Feroz Shah Kotla, KKR first restricted the home team to 146/8 in 20 overs and completed the run chase convincingly with 11 balls to spare.
Gambhir scored a 49-ball 60 and Pathan remained unbeaten on 40 off 26 to power KKR to 147/4 in 18.1 overs. This was KKR's 3rd win of the season in 4 matches. DD have won 2 and lost 3 so far.
Gambhir fell in the 18th over with his team just 3 runs away from victory. Today's knock was Gambhir third half century in IPL 2015.
At the start, Robin Uthappa (13) and Manish Pandey fell cheaply. Pandey collected his 10th duck in IPL, joint most in the tournament's history along with Harbhajan Singh, Amit Mishra and Gambhir.
Umesh Yadav, who took 2/18 and was instrumental in keeping the hosts to a below-par score, was adjudged the Man-of-the-match.
DD restricted to 146/8
Earlier, KKR bowlers led by pacers Morne Morkel and Yadav bowled a tight line to restrict DD to 146/8. Put into bat, DD were hurt by lack of partnerships but a late flourish from Angelo Mathews (21-ball 28) helped the home side get some respect to their total as Morkel and Yadav picked two wickets apiece.
The South African pacer (2-30) drew first blood after getting Mayank Agarwal (1) caught at long leg with Yadav taking a sprawling catch.
Mystery spinner Sunil Narine then struck in his very first over, cleaning up skipper Jean-Paul Duminy (5), who was done in by an off-spinner that was pitched outside the leg-stump to the left-hander. Young batsman Shreyas Iyer (31) then counter-attacked to stitch a 36-run partnership with Manoj Tiwary (32).
Just when it seemed the Mumbai-born player, who hit 3 fours and a six, is ready to take on the KKR bowlers, leg-spinner Piyush Chawla got the dangerman cleaned up in the ninth over.
Tiwary then joined hands with Yuvraj Singh (21) to not only rebuild the DD innings after the strategic time out but also improve the scoring-rate with a few hits to the fence.
But the Bengal player, whose 28-ball stay was laced with 5 fours, was scalped by Morkel after he mis-timed a pull to short mid-wicket as the fourth wicket 37-run partnership came to an end.
Yuvraj falls to a funny stumping
Yuvraj's brief stay at the crease also came to an end in what looked like a funny stumping off Chawla after the left-hander had lost sight of the white ball while attempting a sweep and wicketkeeper Uthappa was sharp to take the bails off only in the second attempt.
KKR bowlers continued to hurt the DD batting after Yadav got Kedar Jadhav (12) caught at backward point on the last ball of his third over.
But Mathews got stuck into Narine, hitting the off-spinner for two consecutive sixes and ended the 19th over with a boundary to get 20 runs of the West Indians' final over.
Nathan Coulter-Nile was run out in the final over of the innings and Mathews was caught behind off the final delivery with Yadav ending with impressive figures of 2-18.
Before start of play, the two teams also observed two minutes silence in memory of young Bengal player Ankit Keshri, who died of a cardiac arrest three days after sustaining head injuries post a freak on-field collision during a CAB one-day game.