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 Behrendoff (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 around 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.
Earlier put into bat, Behrendoff celebrated his World Cup selection by getting the prized wicket of Kohli, who edged to stumper Quinton De Kock.
Parthiv struck three fours and a six off Behrendoff in the fifth over from which RCB amassed 19 runs. But he threw his wicket away, giving a dolly to Suryakumar Yadav off Hardik Pandya (1/21).