Dhoni was at his destructive best, smashing 40 off 26 balls in the death overs to propel Pune to 162 for four before young off-spinner Sundar took three important wickets that led
To Mumbai falling short with 142 for nine in Qualifier 1.
It was Pune's third win over Mumbai in as many games this season, providing them with an opportunity to win the coveted trophy in only their second season.
With the pitch playing unusually slow, anything over 150 was a tricky target despite Mumbai batting deep.
Sundar sent back opposition skipper Rohit Sharma, Ambati Rayudu and Kieron Pollard in a space of 12 balls to leave Mumbai gasping at 51 for four in eight overs.
Parthiv Patel (52 off 40) was solid at the other end and even used the long handle effectively to smash three sixes on the on side.
He eventually ran out of partners with Pandya brothers too back in the pavilion leaving Mumbai at 101 for six in the 15th over. Patel too fell three balls later, leaving the tail- enders to do too much in the end with 60 runs needed off the last 30 balls.
Ajinkya Rahane (56 off 43) and Manoj Tiwary (58 off 48) revived Pune's innings following a bad start before Dhoni finished the innings on a high note, hammering 40 off 26 balls including five sixes.
Mumbai leaked 41 runs in the last two overs bowled by Mitchel McClenaghan and Jasprit Bumrah, who went for 26 and 15 respectively.
Put in to bat, Pune found themselves under severe pressure after losing opener Rahul Tripathi and captain Steven Smith inside the first two overs.
A sharp and full inswinger from McClenaghan ripped through Tripathi's defense while Smith played a loose shot off Lasith Malinga, a mistimed flick that went really high before the ball settled in the safe hands of Hardik.
Rahane and Tiwary were now in the middle to resurrect the innings.
Rahane, who did not score big in the league stage, was determined to make an impact on the big stage.
A couple of boundaries off McClenaghan got him going, the second being a delightful cover drive.
Both Rahane and Tiwary kept the scoreboard ticking but were unable to clear the fence regularly.
Rahane eventually completed his fifty off 39 balls while Tiwary was on 30 off 29 balls when Pune reached 83 for two in 12 overs. To make the situation tougher for Mumbai, Rahane was adjudged leg before off Karn Sharma in the following over.
The visitors now needed the big hits badly to post a fighting total.
Dhoni walked in to join Tiwary and did not take long to hit his first six, depositing a half-volley off Karn Sharma over deep midwicket.
Karn, who was picked ahead of Harbhajan Singh for the crucial game, ended up with decent figures of 4 for 30 in four overs.
Pune got the much needed push in the last two overs courtesy a Dhoni special.
Tiwary too gave him good support during their 73-run stand off 44 balls, scoring four boundaries and two sixes in total.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)