Rising star Morikawa outguns Thomas in dramatic PGA playoff
He then stayed alive by draining a 24-foot birdie putt on the first playoff hole immediately after third-round leader Thomas had made a jaw-dropping 50-foot putt for birdie.
World number five Thomas was trying to win for the 13th time on the Tour, but he was undone on the final hole of the playoff after his tee shot on the par-four 10th sailed right and landed behind a tree.
Thomas closed with a 69 but that included two bogeys in his final three holes after beginning his round with a two-stroke lead over Viktor Hovland, with Morikawa three adrift.
"I am pretty pissed off, it is the only way to explain it," Thomas said. "I had a three-shot lead with three to go and completely handed it over.
"Collin played great. He had a very tough hole at 17.
This week's Workday Charity Open is the first of back-to-back events at the Jack Nicklaus designed Dublin, Ohio course. The Nicklaus-hosted Memorial will follow next week.
After rain, wind and lightning led to two suspensions on Friday, organizers decided to move the tee times up on Sunday to avoid any more weather delays.
Morikawa started Sunday's round three shots back after opening with a 65 and 66 to lead the first and second rounds.
He quickly fought his way back to the top of the leaderboard with two birdies and an eagle in his first five holes.
He made three more birdies on the back nine including the par four 17. Morikawa used an eight iron to spin his approach shot to eight feet then made the putt and celebrated with a fist pump.
His only blemish came on the par-four 13th when he made bogey as he closed with a four-under 66.
- Back-to-back bombs -
Thomas went first, making a 50-foot downhill putt for what appeared to be the victory. But Morikawa wasn't going anywhere. He stayed alive by draining his putt, from just inside 25 feet, to send it back to the 18th tee for a second playoff hole.
Morikawa sealed the win on the 75th hole, two putting on the green after Thomas missed the fairway off the tee and had to chip out from behind a small tree with his second shot.
The win was Morikawa's second in just his 24th start as a pro.
"This is a huge kind of stepping-stone," Morikawa said. "We got number one (win) out of the way, we got number two -- let the gates just open and let's keep going because obviously it was a tough loss at Colonial a month ago, but I learned a lot.
"This is just more positives, more learning for me."