Former Australia captain Steve Smith has finally broken out of his run of bad form with a fine half-century for his struggling Rajasthan Royals side.

But his knock was not enough to stop the AB de Villiers-inspired Royal Challengers Bangalore from racing into the top three of the Indian Premier League with a seven-wicket win.

With Bangalore needing 35 off the last two overs, South African De Villiers hammered three successive sixes off left-arm seamer Jaydev Unadkat's first three balls of the 19th over. The over ended up costing 25 runs.

Chasing the Royals' 6-177, De Villiers finished on 55 not out off 22 balls and brought up victory by hitting Jofra Archer for a big six over midwicket as Bangalore reached 3-179 with two deliveries to spare.

"I want to perform for the team and show the owners I'm here for a good reason," de Villiers said.

"When Unadkat was bowling, I was looking leg side but to be honest I was nervous because I knew I had to hit it well, luckily I got a few away."

Defeat pushed Smith's Rajasthan into a very tight corner, with just six points from nine games and only five matches left.

Earlier, South Africa pacer Chris Morris took 4-26 to restrict Rajasthan to 177-6 despite Smith returning to form with 57 off 36 balls, his first decent knock since he notched back-to-back half centuries in the first two games at Sharjah.

Marcus Stoinis' Delhi Capitals moved to the top of the IPL after Shikhar Dhawan scored his first Twenty20 century and Axar Patel blasted three sixes in the last over to beat Chennai Super Kings by five wickets.

Stoinis contributed a solid 24 off 14 balls.

Faf du Plessis had earlier top-scored with 58 for Chennai, with the total boosted by Ambati Rayudu's 45 off 25, Jadeja's 13-ball knock of 33 with four sixes and Shane Watson's 36 off 28.

Delhi lead the ladder with 14 points after their seventh win in nine games, Bangalore are joint second with Mumbai on 12 points.