With the score tied 21-21, rookie quarterback Christian Ponder drove the Vikings (2-6) 72 yards on 13 plays, setting up Longwell's 31-yard boot.
But Mare shanked it, handing Minnesota the win.
Ponder finished the day 18-for-28 passing for 236 yards and a TD pass while Adrian Peterson scored on the ground and through the air, compiling 162 all-purpose yards for the Vikings.
Newton completed 22-of-35 passes for 290 yards and three TD tosses without an interception for Carolina.
Steve Smith hauled down seven passes for 100 yards and a score in the loss.
Swim Week Miami Beach 2014 [PHOTOS]