The defending champions had to finish the game with freshman Doug Ryan making his collegiate debut in goal after starter Akira Fitzgerald had to leave in the 64th minute with vision trouble following a collision with a William & Mary player minutes early.
The Deacons, who were already without star defender Ike Opara (groin injury) and Austin da Luz (knee injury), outshot the Tribe, 22-6, but both teams had chances to win in regulation.
Arnoux hit the crossbar in the 25th minute, William & Mary's Alan Koger found the post in the 57th minute, and Wake hit the woodwork twice in the span of five minutes later in the second half as Danny Wenzel had a header that hit off the crossbar and Marcus Tracy had a shot that hit off the right post.
In the 95th minute, Tracy played a pass to Arnoux on the right side of the box. Arnoux's shot from just inside the six-yard box got past keeper Andrew McAdams and trickled into the left side of the net for his team-best 15th goal of the season.
"I don't think it's cliché to say hats off to William & Mary for the performance tonight," Wake coach Jay Vidovich said. "They made a tremendous match out of what we call the tournament of champions in the NCAA. I'm very proud of our guys. It was a tough game to play against a very good opponent. The chances didn't fall our way this evening. We lost Ike Opara in the back, but Justin Lichtfuss stepped in and had several blocked shots. Akira went out with concussion issues and Doug Ryan stepped up."