Raina battled cramps on way to his 50-ball knock and shared 46 runs with Albie Morkel (28 not out) to help the defending champions overhaul Bangalore’s 175-4 with two balls to spare at the Wankhede Stadium.
Needing 33 runs to win from the last two overs, Morkel and Raina hammered 21 runs in the 19th over bowled by left-arm paceman Sreenath Aravind to leave Chennai needing just 12 in the last.
Morkel brought off the winning runs with a six off captain Daniel Vettori to cap a memorable outing for Mahendra Singh Dhoni’s men.
Bangalore will get another shot at making the final according to the new IPL format, taking on the winner of the second playoff between Kolkata and Mumbai to be played on Wednesday.
The final will be played in Chennai on Saturday.
Chennai were staring down the barrel after being reduced to 7-2 in the second over but Raina put the innings back on track with a vital 63-run stand with Subramaniam Badrinath (34).
Raina’s innings upstaged a fine effort by Bangalore’s Virat Kohli who hit 70 not out off 44 balls with three sixes and five fours after Dhoni won the toss and elected to field.
Kohli also shared 48-runs for the fourth wicket with Luke Pomersbach (29) to help Bangalore recover from early losses, including the dismissal of explosive opener Chris Gayle for eight.
Gayle, the leading run-scorer of the tournament with 519 runs from 10 just innings, was trapped leg-before by Ravichandran Ashwin while attempting to sweep the off-spinner.
Ashwin, who took a nasty blow on his head while fielding off his own bowling, picked up 1-33 while Doug Bollinger impressed the most among pacemen with figures of 1-20 off his four overs.
Royal Challengers Bangalore 175-4 in 20 overs (V. Kohli 70 not out, Mayank Agarwal 34, L. Pomersback 29) lost to Chennai Super Kings 177-4 in 19.4 overs (S. Raina 73 not out, S. Badrinath 34, MS Dhoni 29, A. Morkel 28 not out; Zaheer Khan 2-31) by six wickets.