Adam Scott made four birdies in five holes after the turn to help him rally and win the Cadillac Championship ahead of American Bubba Watson.
While overnight leader Rory McIlroy struggled home in a two over par 74, Scott carded a 69 at Doral to clinch the win. He also won last week at The Honda Classic.
Rory took a three-shot lead over defending champion Dustin Johnson and Scott into the final round as he looked to join Jack Nicklaus and Tiger Woods as the only players since 1945 to win 12 times on the PGA Tour before the age of 27.
A string of pars was enough for the four-time major winner to edge another stroke ahead when Johnson and Scott both double-bogeyed the third hole as Doral’s Blue Monster course lived up to its name.
However, McIlroy then bogeyed the seventh - his first dropped shot since the second hole of his second round - and found water with his approach to the eighth.
The 26-year-old saved par after taking a penalty drop and pitching to six feet, but failed to repeat the feat after finding sand off the tee on the ninth.
His chances suffered another blow with a bogey on the 13th which dropped him back to nine under, three behind Scott.
He grabbed his only birdie of the day at the short par four 16th and eventually finished the tournament, tied for third, two shots behind Scott.
Rory admitted he was frustrated to let another opportunity slip through his fingers having finished 20th in the Northern Trust Open a fortnight ago after sharing the lead with 16 holes to play.
“I didn’t make enough birdies,” McIlroy said.
“I felt like my game was okay for the most part, but I didn’t take advantage of the holes I should have.
“I couldn’t birdie any of the par fives and that’s really what killed me today. I’ll take a lot of positives from this week. A lot of things didn’t go right for me, but I need to just pick myself back up and get into contention again in Orlando in a couple weeks’ time and let’s see if I can get the win there.
“It’s frustrating because it’s two out of the last three weeks. I’ve got two events left to try to get that win before going to Augusta and I’m hopefully going to get it.”
There was drama for Scott on the last when his second shot finished inside the hazard line but not in the water, and he had to get up and down, sinking a six-foot putt to take the crown.
“I made a couple of horrible errors on the front nine but you can’t give up hope and I thought if I can get a couple of birdies before the turn, maybe a great back nine is good enough if things go my way and they did somehow,” he said.
“I have been working hard on my putting and couldn’t ask for a better way to test myself, a six-footer to win. I can’t believe I have won back to back and to win a WGC is huge. Somehow I need to bottle this up and keep it another four or five weeks through the Masters.”
American Bubba Watson held a share of the lead at the turn with the help of a 60-foot eagle putt on the eighth and hit the front on his own at the 12th, but a closing 68 was not enough to hold off the Scott charge.
Englishman Danny Willett turned in 33 to also be part of a four-way tie at the top before bogeying the 11th and, while birdies at the 12th and 16th reignited his challenge, a dropped shot at the last saw him finish alongside Rory in a share of third.
Graeme McDowell’s final round 75 ended badly with a quadruple-bogey eight.
The Portrush golfer had earlier suffered double bogeys on the seventh and 10th only to bounce back with a run of birdies on the 12th, 15th and 16th. He finished in a tie for 28th while Shane Lowry ended his tournament tied for 35th.