Skipper Flynn smashed his way to 30-ball-53 as his partnership of 90 runs in 9.3 overs for the fourth wicket with glovesman BJ Watling (53 off 37 balls) laid the foundation for a commendable total.
This was after Northern were in a spot of bother at 60 for three by the end of the eighth over having lost the in-form Kane Williamson (14), Amton Devcich (9) and Daniel Harris (20) quickly.
Flynn and Watling first got the measure of the Lions attack by rotating the strike before the launch a furious assault at the rear.
The best shot was a hook by left-hander Flynn when Imran Ali tried a short ball. Flynn went back and across in a flash to hook it behind backward square leg.
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Flynn's 50 came off only 27 balls when he first flashed an Aizaz Cheema delivery behind point and then picked the slower delivery to loft it straight into the sightscreen for a six. He completed the milestone with a single.
Flynn was finally stumped by Umar Akmal off offie Adnan Rasool's bowling as he tried to give bowler charge and missed the line completely.
Watling completed his 50 off 33 balls and was out trying to hit Aizaz Cheema over long-on only to be caught by Ahmed Shehzad. Cheema also removed Scott Styris off the very next delivery, with Shehzad taking an even better catch.