Chasing 162 for a win in the qualifying match, Mumbai rode a clinical 139-run opening stand between Simmons (76 not out) and Hussey (60 off 40 deliveries) to achieve their 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.
But Lendl carried on and in a fitting end, skipper Kieron Pollard (20 no 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.
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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.
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.