Monday at Amoudry National began early, as 74 players tried to cram in their rounds a day late. On the move early: handicapped golfer Will Gainsborough and a resurgent Daniel Bridges. Gainsborough and Bridges had shot 76 and 77 in the third round, respectively, but were quickly clawing their way back into contention. But it was amateur Vivien Mangarelli, playing in the final pairing with tournament host Landry DeChambeau (decked out in his usual Sunday red cardigan, blue pants, and driver cap), who took the solo lead on the front nine with a hot start.
Gainsborough continued to sizzle, carding two eagles in a row at the drivable 15th and par-5 16th to tie Mangarelli at -1. However, a bogey at the 17th put his tournament hopes in jeopardy. He headed to the 18th needing birdie. After his tee shot found the rough, he hit his approach to five feet, receiving a standing ovation from the large crowd as he wheeled himself up to the green. Gainsborough managed to make the birdie putt to post -1 for the tournament.
Crowd favorite DeChambeau quickly dropped shots after making the turn in even par for the tournament, and had stalled at +1 for his round and the tournament through 16 holes after a rough par on the par-5 16th. As the final group moved to the 17th tee, DeChambeau would likely need a birdie-birdie finish to have a chance at the title. Mangarelli had already hit his tee shot at 17 to inside ten feet. DeChambeau hit a disappointing 20 feet and had left himself a tough downhill putt. Playing for six feet of break, DeChambeau rolled in the putt with some pace to move back to even par for the tournament. Mangarelli's putt was completely misread and ended up three feet from the hole, all downhill. The amateur rolled in the putt and headed to the last with a one-shot lead over DeChambeau. Both players found the fairway off the tee. Mangarelli played a conservative shot to about 30 feet. It was now up to DeChambeau to put himself within birdie range. His ball rolled to within five feet of the hole, but spun back and ended up at the bottom of a ridge, about 20 feet from the cup. Mangarelli lagged his putt to the hole and tapped in for par to post 1-under 287 for the tournament. DeChambeau wasted no time hitting his putt. It rolled halfway around the cup and trickled in, prompting a huge celebration on the green. There will be a three-way 18-hole playoff on Tuesday morning.