Ahkeen Williams twice scored in the first half on one-yard runs as the Red Rams raced out to a 12-0 lead. Cortland answered with a big play as, after Williams' second TD, Jon Prior returned the ensuing kickoff 84 yards for a score.
Not fazed by this, Williams led another scoring drive, and when Jake LaRussa found the end zone from five yards out, J-D had an 18-6 halftime lead.
But the Rams went quiet in the third quarter and, during that crucial stretch, the Purple Tigers twice found the end zone as Prior and Brian Strough scored on short runs.
Now trailing 20-18, J-D briefly regained the lead early in the fourth quarter as Alex Hatem, who had a team-high 12 tackles on the defensive side, caught a 21-yard TD pass from Williams and Curtis Walker ran in for two points.
Once again, the Rams could not hold on. Cortland went ahead for good on Devin Darrow's 12-yard TD pass to Justin Hogan, then clinched it minutes later when Darrow scored on a two-yard sneak.
Williams' all-around effort included 100 rushing yards on 20 carries, plus 94 yards through the air as Walker also broke the 100-yard mark on the ground - 104, to be exact.
Now J-D (0-3) will seek its first win of the season at ESM (2-1) as the two neighbors gather on the Spartans' home turf next Friday for a 6:30 kickoff.