Du Plessis and Glenn Maxwell added 120 runs in just 62 deliveries for the third wicket and laid the platform for a big finish. But after Maxwell fell to Jason Behrendorff in the 13th over, Mahipal Lomror and du Plessis also followed suit in the next ten deliveries and Royal Challengers could add just 53 runs in the last 35 balls.
"At least 20 [runs]," du Plessis told the broadcaster when asked how short his team were from a potentially winning score.
"I think in the context of the wickets so far this season it feels like anything under 220 with Mumbai's powerful batting line-up, and obviously they are a strong chasing team and bat very deep," du Plessis said. "So we were very disappointed."
"I think we didn't capitalise in those last five overs. That's when on a wicket like this you can really do some damage. So disappointed with the last five overs and the lack of runs."
"He [Madhwal] was with us last year as well and we saw the skillset he brings. All we wanted to do was give him that specific role so he focuses on that and we told him this is what you have to do," Rohit said at the post-match presentation ceremony.
"I know these are tough overs to bowl but he's quite confident. When I speak to him, the responses that I get, he is quite confident. He is a leader as well. He leads his Uttarakhand team. So he has got a lot of knowledge about how he wants to bowl, what sort of field placements he wants to have."
Rohit also said that Royal Challengers looked set for a score in the region of 220 and praised his team for reining things back in the last few overs, something which the team has struggled with this season.
"It was crucial what we did there at the back end. Restricting them to less than 200 was a great effort," Rohit said. "At one stage it was looking 220 or something like that and the way we have bowled in the last part, it could have been 220 or maybe more."
Du Plessis: 'Suryakumar makes a captain extremely grey'
In the chase, Ishan Kishan got Mumbai Indians off to a blinder as he smashed his way to 42 off 21 deliveries. But Hasaranga had him caught behind and then trapped Rohit lbw in the fifth over.
Suryakumar hit six sixes and seven fours to help Mumbai complete the chase in 16.3 overs -- the quickest that a target of 200 or more has been chased down in the IPL.
"He [Suryakumar] is one of the best isn't he? When he gets going, he's really difficult to bowl to," du Plessis said.
"He makes a captain extremely grey because he's got so many options. You don't feel like you can really shut him down," he said. "That's why I said he is one of the greats at the moment."