Chasing 172 for a win, the match was in a balance when he came out in the 16th over but Hardik, who was named in Indias World Cup squad on Monday, turned the game on its head, smashing five boundaries and two sixes during his unconquered 16-ball innings on a turning track at the Wankhede Stadium.
Mumbai needed 22 runs from the last two overs but Hardik took just six balls to hit the required runs, smashing left-arm spinner Pawan Negi for two boundaries and as many sixes to end the run chase. He finished the game with a single off the last ball of the 19th over as Mumbai reached 172 for 5 in 19 overs.
This was Mumbais fifth win in eight games and they are now at third spot with 10 points, while RCB suffered their seventh defeat in eight matches and the Virat Kohli-led team are languishing at the bottom of the table.
Earlier, veteran Sri Lankan pacer Lasith Malinga took four wickets for 31 runs as Mumbai restricted RCB to 171 for 7. Mumbai were off to a flying start in their run chase with openers Rohit Sharma (28) and Quinton de Kock (40) finding the boundaries with ease.
De Kock took 16 runs from the third over bowled by Umesh Yadav, smashing two boundaries and a six while captain Rohit was elegant as ever, hitting a four and a six off Mohammed Siraj the next over.
Mumbai were wallopping at 67 for no loss at the end of first powerplay overs but suddenly off-spinner Moeen Ali (2/28) brought RCB back into the match with a two-wicket burst in a single over.
The Englishman removed the two set openers Rohit and de Kock in the space of four deliveries in the eighth over. Rohit was done in a by a delivery which turned viciously from the offside while de Kock was plumbed in front as he was beaten by a delivery which skidded instead of turning and Mumbai were 71 for 2 in 7.4 overs.
Ishan Kishan (21) came out and nonchalantly smashed two sixes off Negi before he fell to Yuzvendra Chahal (2/27), stumped by Parthiv Patel.
The Mumbai run chase started stuttering and with the pitch turning, Suryakumar Yadav (29) and Krunal Pandya (11) was finding it difficult to get the boundaries. Play was held up for a few minutes in the 13th over with Chahal seemingly having some problem on his little finger but he returned to bowl his fourth over and had the wicket of Suryakumar who holed out to Navdeep Saini near the boundary.
Hardik was nearly out in the 17th over but it was his elder brother Krunal who was out in the next over off the bowling of Mohammed Siraj. It was then left to Hardik to take Mumbai to victory in a dramatic fashion. Earlier, AB de Villiers and Moeen Ali hit impressive half centuries to guide Royal Challengers Bangalore to a respectable 171 for 7 after being put into bat.
After RCB lost skipper Virat Kohli (8 off 9 balls) and Parthiv Patel (28 off 20 balls) inside seven overs, de Villiers (75 in 51 balls) along with Ali (50 runs in 32 balls) resurrected the innings with a 95-run stand for the third wicket.
The South African star stamped his authority, hammering six fours and four sixes, as he completed his half-century in 41 balls. Ali was a little bit more aggressive than De Villiers as he hit five sixes and a lone boundary as the two took the MI attack to cleaners.
Ali initially played second fiddle but later upped the ante. He was particularly severe on Australian pacer Jason Behrendorff (1/49), whom he hit for two sixes and a four in the 16th over, which fetched 17 runs for RCB. De Villiers, who took time to settle, then showed his class, as he hit round the park.
However, veteran Sri Lankan pacer Lasith Malinga (4/31) pegged the visiting side back by removing Ali and Marcus Stonis (0) in the 18th over and taking two wickets in the final over. De Villiers was run out in the final over off a brilliant throw from long-on.