(CNN) -- Phil Mickelson fought off a nasty virus and his co-overnight leader Nick Watney to land the WGC-CA Championship on the Blue Monster Course at Doral.
Mickelson holds the winning trophy aloft after a last-day battle in Florida.
It was the second title of the year for Mickelson, who had been treated for heat exhaustion and dehydration before carding a last day 69 for a 19-under total of 269.
Watney finished a shot back, coming up a fraction short with a birdie putt on the tough 18th which would have forced a playoff.
World No.1 Tiger Woods produced his second 68 of the weekend to finish tied for ninth on 11-under in the first strokeplay event of his comeback.
Jim Furyk provided the last-day challenge to the leaders with a closing 67 for 16- under, with India's Jeev Milkha Singh fourth at 14-under and England's Oliver Wilson tied fifth with Colombia's Camilo Villegas after a brilliant closing 66.
Miickelson was claiming his first World Golf Championship victory, coming hard on the heels on his win at the Northern Trust Open in Los Angeles.
"I fought hard all day and wasn't really able to pay attention to some of the great shots that Nick hit because I was so worried about keeping my energy level high and steady throughout the round," Mickelson told the Press Association. "I haven't eaten much in three days and I fought hard. I knew I was playing some of my best golf coming in here and I was playing well so I'm very excited to have finished it off."
The lead had changed hands three times between Mickelson and Watney over the front nine with Watney holing in a chip at the ninth from 80 feet to stay in the hunt.
A bogey on the 11th saw Watney trail again and after both men bogeyed the 12th it was left for Mickelson to hold his nerve in the closing holes.
Both men hit fine shots to the closing par-four hole, with Watney's putt coming up agonizingly short. "I can't believe I left it short," he said. "Unfortunately I just didn't hit it hard enough.
"I'm pleased with the way I played. Right now it still hurts to finish second -- disappointing to come up one shot short. But overall it was a positive week, and I've just got to keep working hard."
Northern Ireland teenager Rory McIlroy slipped off the pace in the final round with a one-over 73, but still achieved his second consecutive top-20 finish in his debut on the PGA Tour.
He was bracketed at nine-under with, among others, Luke Donald (72), Ernie Els (70), Padraig Harrington (71) and Justin Rose (68).