CASTLE STUART, July 14, 2013 (AFP) - Mickelson, and the highest world ranked player in the field, captured his 50th pro career success after defeating South African Branden Grace with a birdie at the first extra hole.
Both players had ended regulation play tied at 17-under par with Grace posting a 69 and finding his way into the play-off when Mickelson horribly three-putted the last hole for bogey in a round of 68.
However Mickelson then brilliantly played one of his trademark wedge shots landing his 45-yard third shot a few feet past the hole before the ball spun back to some six inches from the cup for the easiest of birdies, while Grace missed his birdie putt from 25-feet.
Mickelson had lost the event in a play-off six years ago at Loch Lomond but has finally captured the event in his ninth Scottish Open appearance.
"I've been coming to Scotland now for quite some time and I've enjoyed my stay every year. I've had some opportunities before and I almost let it slide away today," he said.
"So to come out on top feels terrific and this Castle Stuart golf course is just wonderful and I've had so much fun here the last three years, so to win means a lot to me.
"I was so mad at myself for losing my focus and three-putting the last hole in regulation play so I went back to the 18th hole for the play-off pretty focussed to make a four."
Mickelson, who collected a first prize cheque for $742,800 (580,000 euros), now will stand firm as a favourite at the 142nd British Open championship starting Thursday at Muirfield to the east of Edinburgh.
The American was third in the 2004 British Open at Royal Troon and joint runner-up two years ago at Royal St. George's.
"This week has been very valuable for next week as I did a lot of things well and also there are a few things I still need to work on," he said.
"But then today was a great day for us to have this type of windy weather as the first three days were very benign and it didn't have the teeth this golf course can have on a day like today.
"So I am anticipating this kind of weather next week at Muirfield, and if we (do) have it (then) today was very important for me getting ready."
Mickelson's only victory in Europe prior to the Scottish Open was in 1993 when he captured a secondary Challenge Tour event near Euro Disney in Paris.
"Mickelson is a great player and he's not going to mess it up on the last," said Grace.
"I'm still pleased, played well, put myself in contention and it's a good week heading into next week.
"I was playing maybe for third or something, and it just shows how quickly things can change out there."
Danish rookie J B Hansen and Sweden's Henrik Stenson both shot 71s to share third place on 15-under par.
Hansen dropped four shots with a quadruple bogey at the second hole and then raced into a share of the lead with seven birdies over his next eight holes.
After three years at the Castle Stuart course in Inverness, the tournament is moving in 2014 for just one year east to Aberdeen and Royal Aberdeen that hosted the 2011 Walker Cup.
Leading scores from final round of the Scottish Open at Castle Stuart on Sunday (par 72; GBR and IRL unless stated):
271 - Phil Mickelson (USA) 66 70 66 69 (Mickelson won at first play-off hole), Branden Grace (RSA) 71 65 66 69
273 - Joachim B Hansen (DEN) 68 65 69 71, Henrik Stenson (SWE) 70 64 66 73
274 - John Parry 64 72 66 72, Gareth Maybin 69 70 64 71, Martin Laird 68 69 69 68
275 - Nicolas Colsaerts (BEL) 70 68 68 69, Raphael Jacquelin (FRA) 68 70 65 72
277 - Peter Uihlein (USA) 67 66 70 74, Marcel Siem (GER) 67 69 72 69
278 - Brooks Koepka (USA) 70 68 68 72, Hennie Otto (RSA) 70 70 66 72, Eddie Pepperell 69 69 68 72, Simon Dyson 70 69 69 70, Christopher Doak 66 66 73 73
279 - Ricardo Gonzalez (ARG) 70 68 68 73, Tommy Fleetwood 70 67 68 74, Lorenzo Gagli (ITA) 67 67 70 75, David Lynn 69 70 68 72, Victor Dubuisson (FRA 68 66 74 71, Simon Khan 65 69 70 75, Seve Benson 69 69 71 70
280 - Paul Casey 70 67 68 75, Ross Fisher 68 65 73 74, David Horsey 69 67 71 73, Joakim Lagergren (SWE) 71 67 72 70, Morten Orum Madsen (DEN) 70 67 70 73, Paul McGinley 67 72 70 71, Alvaro Quiros (ESP) 68 71 68 73