The Big Green tied the score at 31 after Alex Gakenheimer kicked a 35-yard field goal. Yale went three-and-out on its next possession, and Dartmouth drove 11 plays in four minutes for Williams' game-winning score with 2:13 left to play.
Yale (3-1, 1-1 Ivy) was at the Dartmouth 37 on its final drive, and Morgan Roberts threw three incomplete passes to make it fourth-and-10 with 51 seconds left to play. Roberts' pass to Deon Randall was incomplete and the Big Green took over, running out the clock for the win.
Williams threw for 388 yards and three touchdowns, and picked up one more on the ground. Ryan McManus had 12 receptions for 188 yards and one touchdown for Dartmouth (3-1, 2-0).