Chasing 162 for a win, the Kieron Pollard-led Mumbai rode a smooth 139-run opening stand between Lendl Simmons and Mike Hussey (60) to achieve the target in 16.2 overs.
The veteran Australian left-hander, hitting 5 fours and 3 sixes, and West Indian Simmons, his 51-ball knock laced with 11 fours and a six, combined like fire and ice to make batting look simple and the Express bowling attack look pedestrian.
Hussey's charge ended in the 15th over with leg-spinner Sachith Pathirana getting him caight at deep square leg.
But Lendl carried on and in a fitting end, skipper Kieron Pollard (20 not out) hit two powerful sixes to complete the formalities for Mumbai, who had lost their first qualifier against Lahore Lions.
Earlier put into bat, Southern Express rode Farveez Maharoof's 22-ball 41 to post 161 for 6 in 20 overs.
Maharoof though was given a huge life by Shreyas Gopal, who dropped the all-rounder on 6, after spilling a sitter at long-off on Pragyan Ojha's bowling.
The lanky player made the most it as he hit 3 fours and 2 sixes and stitched a crucial 58-run sixth-wicket partnership with Angelo Perera (28) to give the visitors respectability after losing half their side for 90.
Mumbai new-ball bowlers, Harbhajan Singh (0/18) and Jasprit Bumrah (1/23) bowled a tight line to restrict the batsmen to just 27 runs in the powerplay overs. Bumrah drew first blood in the fourth over of the innings after scalping opener Kusal Perera, who got a top edge as Gopal caught a skier, for 8.
Left-handed opener Danushka Gunathilaka then tried to do the grinding with new-man Yashodha Lanka. The duo stitched a 27-run second-wicket partnership before Pollard (1/18) took matters in his own hands.
Medium-pacer Pollard's slower delivery sent Lanka back in the pavilion after being caught by Ambati Rayudu for 9 in the eight over.
The slide continued till Maharoof stepped to counter attack.