Sweden's Hanson and Larrazabal of Spain were tied at 12-under par heading into the 18th hole of the final round, but Hanson drained a 35-foot putt on the par-5 closing hole to go up by two shots.
Larrazabal, playing in the next group, was faced with trying to match Hanson's eagle to force a playoff but his third-shot chip missed the hole by a few feet.
That gave Hanson his fifth career European Tour win with a final round of 3-under 67, finishing at 14-under 266.
Third-round co-leader Larrazabal parred the 18th for an even-par 70, ending at minus-12 along with last week's European Masters winner, Richie Ramsay (67).
Another third-round leader, Scott Jamieson, fired a 1-over 71 Sunday, taking fourth place at minus-11.
Swim Week Miami Beach 2014 [PHOTOS]