Mickelson failed to make the playoff after he had bogeys at Nos. 16 and 17 that led to a final round of one-over-par 73 and a third-place finish. He did have a chance to make the playoff at No. 18, but he missed a 20-foot birdie putt.
"I'm pretty bummed out," Mickelson said. "I thought that this was one I had in control. If I could have gotten that bunker shot up and down on 15, I would have had a two-shot lead heading into those last three holes, which I know are difficult holes, so it would have been nice to have that.
"There is just no excuse. It wasn't easy, but it wasn't anything out of the ordinary or difficult. I should have made par."
Several big-name players faded on Sunday.
Ernst, playing in only his ninth
Ernst won the tournament on the first playoff hole, No. 18, with a par. Lynn found the rough near a creek with his drive and put his approach in a greenside bunker, from where he sent his next shot over the green back into the rough. His chip for par ran several feet past the hole. Ernst drove into the fairway and then struck a six-iron from 190 yards to within 15 feet of the pin, winning with a tap-in par.
"The feeling is unbelievable right now," said Ernst, who earned $1.2 million for the win and a two-year exemption. "I didn't think about what I had to do or what I didn't do. I just thought about each shot. What is the next one? How am I going to get this next one in the hole? So that was big."