Rohit stitched two crucial partnerships, first a 49-run stand with Quinton de Kock for the opening wicket and then another 88 runs for the unconquered second wicket with Suryakumar Yadav (46 not) as MI chased down the target of 134 with 3.5 overs to spare.
The MI captain carried his bat through the innings, hitting eight fours off 48 balls while Yadav consumed 27 balls for his unbeaten 46.
MI ended the league phase with 18 points from 14 matches -- the same as Chennai Super Kings and Delhi Capitals -- but they secured the top spot by virtue of better run rate. MI ended at a net run rate of 0.421 as against 0.131 and 0.044 of CSK and DC respectively.
MI's win meant that the KKR are knocked out of the tournament with Sunrisers making it to the play-offs at their expense on better net run rate.
KKR and SRH ended the league phase on 12 points each but the Hyderabad-based side sneaked to the play-offs with 0.577 net run rate against 0.028 of the Kolkata side.
MI and Chennai Super Kings play against each other in Chennai in the Qualifier 1 on Tuesday while Delhi Capitals -- who finished third -- take on SRH in the Eliminator at Visakhapatnam on Wednesday.
The Qualifier 2 -- between the losing teams of Qualifier 1 and Eliminator -- will also be played at Visakhapatnam on Friday.
Chasing 134 for a win, MI made a good start with 46 runs coming form powerplay without losing any wicket. South African Quinton de Kock hitting two consecutive sixes and a four off Andre Russell in the fourth over was the highlight.
De Kock (30) was out the first ball after powerplay with wicket-keeper Dinesh Karthik taking a brilliant running catch off the bowling of Prasidh Krishna.
That was the only success KKR had as Rohit and Yadav took MI home in 16.1 overs. Yadav hit a towering six to end the match.
Earlier, Kolkata Knight Riders failed to deliver when it was need the most as they managed to score a sub-par 133 for 7 in their 'do-or die' IPL game against Mumbai Indians on Sunday.