Billy Davies' side arrived at Watford on the back of three wins and three clean sheets and took an early lead through Andy Reid.
But if anyone was going to be the first player to score against Forest this season then McGugan was that man. He hit 44 goals - many of them spectacular - during seven years in Nottingham before a summer move to Watford.
Both sides had chances to win it with Manuel Almunia saving well from Jamie Mackie and Karl Darlow denying both Sean Murray and Ikechi Anya.
A point was enough to send Forest back to the summit but they almost stole all three at the death when sub Ishmael Miller broke clear only to curl his effort against the post.
The home side had led through Grant Holt's early penalty, but found themselves trailing when George Friend equalised before half-time, with Grant Leadbitter putting the Teessiders ahead inside the final quarter.
Gomez, though, ensured a share of the spoils when he drilled home a brilliant free-kick five minutes from time.