Captain Gambhir led a remarkable recovery with a resolute batting display with Mithun Manhas (25 not out) after his side made a messy start in the run chase of 113 by losing their top three batsmen for just six runs in the second over.
The duo shared 75 runs from 70 balls for the unfinished fifth wicket as Delhi romped home with eight balls to spare and snap their three-match losing streak at M A Chidambaram Stadium.
Gambhir, who fought dehydration by applying water on his head and body on few occasions, struck five fours in his 56-ball innings, his second IPL 3 half century, and hit the winning runs, a two, as Delhi reached 113 for four in 18.4 overs on a pitch which offered turn to slow bowlers.
Earlier, Chennai Super Kings could make just 112 for nine after electing to bat with left-arm pacer Ashish Nehra taking three wickets for 26 to lead a superb bowling display by Delhi Daredevils.
With the win on Thursday, their seventh in 13 matches, Delhi are virtually in the semifinals with 14 points. They play Deccan Chargers at home in their last league match on April 18.
Despite the loss, Chennai are still not out of semifinal race with 12 points from 13 matches though the paltry total after batting first took down their net run rate to plus 0.270.
Pacer Dough Bollinger was the most successful bowler with two wickets for 24 runs in his four overs while Ravichandran Ashwin and Shadab Jakati got a wicket apiece.
Delhi made a disastrous start in their run chase, losing their top three wickets for just six in the second over and looked like throwing away the match before Gambhir and Manhas rescued them.
On a track which offered turn to slow bowlers, Chennai opened bowling with a spinner and Ravichandran Ashwin did not disappoint his captain Mahendra Singh Dhoni by removing dangerous David Warner in his third ball for a duck.
Warner tried to play a cut shot but failed to negotiate the turn Ashwin extracted and the ball spooned to cover for Murali Vijay to take a diving catch.
Virender Sehwag (4) played his characteristic style and fell the same way as he has been doing for a while in IPL 3, out cheaply for four after playing a big shot early on as the thick edge off Doug Bollinger’s first ball was easy picking for Matthew Hayden at slip.
Three balls later, Tillakaratne Dilshan (1), who returned to playing eleven after being dropped due to poor form, did not last long as he tried an expansive shot off Bollinger only to see inside-edging the delivery and his furniture being disturbed.
Gambhir and wicketkeeper-batsman Dinesh Karthik started the repair work by sharing 32 runs from as many balls for the fourth wicket before the latter was out for a 16-ball 13 in the seventh over.
Karthik top-edged a pull shot off Jakati for S Badrinath to take a well-judged catch at midwicket to reduce Delhi to 38 for four.
The early wickets saw run rate plummeting and Delhi were 56 for four at the halfway mark. After Karthik’s dismissal Gambhir and Manhas did not have a four for five overs as they ran mostly for singles.
The duo opened up from the 16th over onwards and struck some lusty blows off Ashwin, Suresh Raina and Bollinger to ease past the target of 113 with eight balls to spare.
Manhas gave able support to Gambhir and his 32-ball 25 contained two fours.
Earlier, left-arm pacer Ashish Nehra took three wickets for 26 to lead a superb bowling display by Delhi Daredevils as they restrict Chennai Super Kings to a paltry 112 for nine.
Needing to win the match for a semifinal berth, Chennai failed to apply themselves against a disciplined Delhi bowlers as their top six batsmen were back at the hut by the halfway mark for just 55 runs after electing to bat.
S Badrinath top-scored with a 29-ball 30 while Murali Vijay (17), Suresh Raina (15) and Michael Hussey (15) got the starts but failed to convert them to big scores as Chennai slumped to their lowest IPL 3 total.
For Delhi, Nehra took important wickets of openers Vijay and Matthew Hayden and that of Badrinath in his four overs. Sehwag chipped in with a superb two for 18 from his four overs while Dilshan, Amit Mishra and Dirk Nannes got one each. (PTI)