"I beat two of the three most talented guys in my era," said Larrazábal, who likened his birdie putt on the 18th to the par putt holed by Martin Kaymer to retain the Ryder Cup at Medinah in 2012.
"The first win in France my brother says was the win of talent. I had 100 putts in 72 holes, not even the best Tiger Woods could have beaten me that week.
"The second win in Munich (in a play-off with Sergio Garcia) was one of belief. This is the win of hard work and team work. I worked so hard for the last two years and over the winter and I beat two of the three most talented guys in my era."
Starting the day three off the lead, Larrazábal birdied the second from eight feet and almost aced the par three fourth.
With overnight leader Craig Lee stumbling, the lead switched hands on a regular basis but the 30 year old Spaniard fell behind the likes of McIlroy and Mickelson with a bogey at the fifth.
He chipped to a foot from the bunker at the eighth and sunk a six footer at the 11th to remain in touch, although Mickelson looked to be in command with three birdies over his first ten holes.
But the Open Champion hit a three wood left under a bush on the 13th and decided to try and play back-handed rather than taking a drop.
The ball only bobbled up and caught his club on the follow through, and with a penalty drop the World Number Five was left to play his fifth shot to the green before two putting for a triple bogey seven.
That opened the door to the chasing pack, and it was Larrazábal who marched through it with a brilliant pitch to within a foot from the rough at the 13th before firing to the heart of the 18th green in two.
A poor first putt created some tension, but the former Sir Henry Cotton Rookie of the Year converted the second to take his third European Tour title.
“It feels great,” said Larrazábal. “Only me and my team know how much we’ve worked during the last three years.
“I want to thank so many people starting with my brand Callaway – they set up a driver I hit 20-25 metres further. Then I want to thank my team and my girlfriend. It’s just unbelievable.
“The birdie at 13 gave me the confidence to keep it going and I hit great shots coming in. The five wood at 18 is maybe the best shot of my golfing career.”
McIlroy produced a closing 68 to finish tied for second with Mickelson, who recovered brilliantly to birdie three of his last five holes.
The Northern Irishman was left to rue both a string of missed birdie chances after some wonderful work from tee to green, and his two shot penalty in the third round for an incorrect drop.
“It's frustrating - I've played well the whole week,” admitted the World Number Seven. “It's a very positive start to the season so I'm not going to let one little negative ruin that.
“I came in here telling everyone that I'm really happy with my game and done some good work and felt like it was coming together for me at the end of last year. I've continued that on, so I’m really excited for the rest of the season.
“I’ve got a week off now to prepare for Dubai and give it another run there and see if I can get the win there.”
George Coetzee and Rafa Cabrera-Bello finished tied for fourth on 12 under, whilst Swedish rookie Johan Carlsson produced the round of the day with a 65 to record a top-ten finish.
Lee eventually signed for a 77 to finish in a tie for tenth.