The win was Havret's second on the European Tour. He closed with a 68 to join Mickelson in the extra session as they finish one stroke clear of Ernie Els.
However, the playoff would not have happened had Mickelson not made bogey on the 72nd hole.
Several big names will join Havret and Mickelson at Loch Lomond this week. They will be joined in the field by the likes of Angel Cabrera, Luke Donald, Els, Miguel Angel Jimenez, Colin Montgomerie and Adam Scott.
Of that group, Els is a two-time winner at the event and Monty won the 1999 title, the year before Els claimed his first win.
Loch Lomond will host for the 13th straight year.
GOLF CHANNEL will have three hours coverage of all four rounds this week. Next week is the British Open Championship, where Padraig Harrington was a playoff winner over Sergio Garcia last year.