Stuard never bogeyed a hole throughout the tournament on the long (7,425-yard), par-72 TPC Louisiana course, which was drenched with more than 4½ inches of rain during the tournament. Weather delays on Thursday, Saturday and Sunday not only forced a Monday finish but also led officials to shorten the tournament to 54 holes.
"I wasn't playing great. I was just kind of, I don't know ... hanging around," Stuard said after his final-round 69. "I kind of hung in there all week. I just didn't get too ahead of myself and just stayed real patient, and it paid off."
Lovemark, Stuard and Byeong-Hun An entered the playoff at 15 under par.
An unraveled on the first playoff hole and Lovemark on the second while Stuard remained steady, virtually clinching the win with a 160-yard approach to within 2½ of the pin for an easy birdie putt.
Stuard's best previous PGA Tour finishes were a pair of second places in Mexico, one in 2010 and the other in 2014.
Lovemark came in with only five career top-10 finishes, but four of those had come this season for the Californian.
"I just wish it was 72 holes," said Day, who finished before the leaders. "At least I gave myself an opportunity to be around the leaders."
The slow, waterlogged course rewarded the players most adept at hitting long in the air off the tee and aiming right for the pin on approach shots. On many shots, balls hardly moved upon landing.
Lovemark and Stuard each birdied the par-5 11th by sticking approach shots within 3 feet. Lovemark drained a tougher, 10-foot, 4-inch putt on 13 to take a one-shot lead he maintained until An and Stuard both birdied the 18th.
Players sometimes struggled to gauge abnormally slow greens. It happened to Lovemark when he left a 9½-foot birdie putt for the win just inches short on the 18th green, dropping him into the playoff.
The narrow miss seemed to unsettle Lovemark, who hooked his drive into the rough on an embankment left of the fairway when the first playoff began on the 18th tee. His next shot found more rough on a sharp downhill lie on the edge of a bunker. But he was able to loft a wedge to 12 feet, helping him force a second playoff hole on the par-5 18th. Lovemark wound up in the rough again, however, then hooked an approach into a muddy area near the grandstand, all but ending his bid to win.
"I feel good," Lovemark said after his best finish since his only other second place in 2009. "Not too disappointed. Just a little bummed, but moving on to next week."
An did not look like a contender entering Monday, but he rocketed up the leaderboard with birdies on 11, 13, 14 and 15. His 5-foot birdie putt on 18 landed him in the playoff -- marking only his second top-10 and his first top-3. But he botched consecutive approach shots on the first playoff hole, leaving him with a bogey that ended his tournament.
Bobby Wyatt, a 23-year-old making his ninth PGA Tour start on a sponsor invitation, had a highlight-filled final round split between Sunday and Monday to nearly take his first victory.
He briefly surged into the lead with an eagle and six birdies on his first 13 holes. He made every green in regulation in his final round, but three-putts for bogeys on the par-3 14th and par-4 15th cost him.
"I certainly haven't been in this position a lot, so I think probably some of it is nerves," Wyatt said.
A birdie on 16, highlighted by a 138-yard approach shot to within four feet of the hole, followed by a 7-foot putt on 18 for his eighth birdie of the round, left him alone in fourth at 14 under.
He still felt like a winner in the big scheme of things. His first top-10 finish qualified him for a 10th Tour start at the Wells Fargo Championship in Charlotte later this week.
"I found out I can play with these guys," he said.