It took three playoff holes, but James Hahn ended Sunday solo atop the Northern Trust Open leaderboard.
The three players finished regulation at 6-under 278. Casey, who overcame a shank on the 13th hole and made what turned out to be a critical par, hit a poor tee shot at the last that led to a bogey that cost him the win. Hahn and Johnson, who each shot 2-under 69 on Sunday, made par on the long finishing hole.
In the playoff, all three players made par in their second crack at No. 18 on the afternoon. Casey got up-and-down for par from off the green, with two-putt pars for Hahn and Johnson.
The extra session moved to the short par-4 10th, with all three players in precarious position to the right of the treacherous green. In succession, all three players hit good shots, with Johnson last to play and ending up closest to the hole. After Casey missed for birdie, Hahn and Johnson poured theirs in to extend the playoff to a third hole, the par-3 14th.
Both Johnson and Hahn found the green with their tee shots. Hahn, putting first, drained the left-to-right-breaker for birdie. When Johnson's attempt to match didn't scare the hole, Hahn had won.
Third-round leader Retief Goosen stumbled on Sunday, shooting 4-over 75 in weather conditions that deteriorated as the day progressed.
Sergio Garcia needed a pair of pars on the final two holes to pick up his first win since the 2012 Wyndham Championship, but made bogey on both instead to come up a shot short of the playoff.
Hahn is now in the Masters and has a two-year exemption on the PGA Tour -- and finally something for people to remember him for other than his Gangnam Style dance at the Phoenix Open.