Buttler struggles but Parag and Sen do the damage for Rajasthan Royals
Buttler has been in immaculate form in the Indian Premier League, scoring successive centuries in the previous two matches, but he lasted just nine balls in Pune on Tuesday.
The England international's score of eight included one boundary before he was dismissed by Josh Hazlewood (2-19) in the fifth over.
Sanju Samson struck an entertaining 27, including three sixes, to get the Royals back on track, though it was Parag who ultimately dragged them through.
Having anchored the back half of the Royals' innings, Parag let rip in the final over, plundering two sixes and a four to get his side to 144-8.
Faf du Plessis elected to go with Virat Kohli at the top of the order, but RCB's former captain went for nine in the second over.
Du Plessis tallied up 23 before he fell to Sen, who had Glenn Maxwell for a golden duck with the next delivery.
Ravichandran Ashwin (3-17) joined the party, dismissing Rajat Patidar, Suyash Prabhudessai and Shahbaz Ahmed, while Dinesh Karthik was run out.
Wanindu Hasaranga (18) offered some resistance for RCB, though their hopes of avoiding a second straight defeat ended when Sen wrapped up the tail as Rajasthan went top of the IPL on 12 points.
Parag takes up the mantle
With Buttler failing to ignite, Parag initially showed great composure before that explosive final over when he reached a 29-ball half-century. Harshal Patel, who took 1-33, was the unlucky bowler, with 18 runs coming from those last six balls.
More frustration for Kohli
It was another bad day at the office for Kohli, who has failed to reach double figures in five of his nine IPL innings in 2022. Indeed, it was a bad day all round for the Challengers, who could have gone top with a win, with only Du Plessis scoring above 20.