Morikawa pulled into a tie with Thomas (-3) after the latter saw his potential winning putt on No. 18 sail wide of the hole.
Thomas, the No. 5-ranked player in the world, did not record a bogey in his first three rounds before notching four on Sunday, including two over his last three holes prior to the playoff.
Thomas recorded back-to-back bogeys on Nos. 2 and 3 on Sunday before getting back on track. He recorded birdies on Nos. 10 and 11 with another on No. 14 and an eagle on the following hole.
Of the 12 previous occasions Thomas held or shared the 54-hole lead, he went on to win the tournament eight times.
Norway’s Viktor Hovland (71) finished third at 15-under 273, followed by Chase Seiffert (67) at -14. Great Britain’s Ian Poulter (70) and Gary Woodland (67) tied for fifth at 12 under.
–Field Level Media