Davis missed set pieces to win on each of the playoffs. The 26-year-old Australian left 6- and 18-foot set shots high, a set 25 feet low and a height of 19 feet. He misread a break on a 12-foot shot on the fifth playoff, and then won when Merritt wandered.
Davis finished with a 5-under-67 to Merritt (68) and Joaquin Niemann (68) at 18 under 270 at Detroit Golf Club. Niemann falls out of the playoffs with a thug on the first extra hole, his first boogie of the week.
Niemann had a chance to win it on the 72nd hole, but he left a shot 17 feet high.
Davis stabbed a 50-foot sandbar for eagle on the 17th par-5 and birdied the par-4 18th to come down on 18th.
Niemann follows with two shots running 569 yards and he assists twice from 14 feet to take the lead at 18 under, but he is quick company.
Merritt, who was with Niemann in the final group, made his fourth birdie in a five-hole piece to share the lead. Davis joined them in the Eagle Bird finish.
The 22-year-old Niemann shared the lead in the second and third rounds and was the runner-up for the third time, among other things in a play-off match at the Sentry tournament for champions.
Last week during the Travelers Championship, Harris Engels knock Kramer Hickok in a playoff game of eight holes that tied the second longest sudden death in the history of the PGA Tour. Hickok held on to watch the playoffs in Detroit after being 6 down.
Alex Noren (64) had a lead at 17. He lost the heat and humidity, but plans to leave the comfortable clubhouse as soon as someone was once in front of him, and this happens to a trio of participants. Noren tied for fourth with Hank Lebioda (68).
Bubba Watson earlier on the hot and steamy afternoon went up the leaderboard with a 64 to put him at 16 bottom. That briefly gave him a share of the lead, and he drew for the sixth Brandon leaves (68).