Gill runs came off just 50 deliveries and there were good enough contributions around the skipper as the Titans chased down a target of 181 with two balls to spare.
Jos Buttler struck 25 while opener Sai Sudharsan scored 22 in a stand of 57 with Gill for the first wicket.
Rahul Tewatia (7 not out) and M Shahrukh Khan (3 not out) were left to finish the job in the final over as the Knight Riders slipped to a fifth defeat in six games.
Earlier, the visitors posted a total of 180 all out thanks largely to 55-ball 79 from Australia allrounder Cameron Green.
They were pegged back by losing wickets at regular intervals during the innings with Proteas star Rabada bagging 3-29 in his four overs.
Rabada was well supported by India paceman Mohammed Siraj (2-23) while Ashok Sharma also took two wickets.
Proteas batter Connor Esterhuizen is set for his first taste of the Indian Premier League after being signed by Gujarat Titans as an injury replacement for the remainder of the season.
Mumbai Indians head coach Mahela Jayawardene says his team need to find a "spark" after they slipped to their fourth consecutive defeat in this season's Indian Premier League.
In a classic Wankhede run-fest on Thursday night, Punjab Kings produced a clinical chase to dismantle Mumbai Indians by seven wickets with 21 balls to spare in IPL 2026's 24th match.
Royal Challengers Bangalore secured their fourth victory of the Indian Premier League season after beating Lucknow Super Giants by five wickets at the M Chinnaswamy Stadium.
