Matthew Hinson, 28, could be sentenced to life in prison for the murder of William Pettry of Lake Villa, Illinois.
Pettry, 42, was visiting Jacksonville to watch the Bears-Jaguars game with a friend who said Hinson had joined them at the table before the stabbing.
Prosecutors had argued that Hinson became jealous when he saw Pettry speak with his wife.
Pettry died after he was stabbed in the neck.
Hnson pleaded guilty to second-degree murder.