Grant Holt made a dream debut as Forest kept in touch with the play-off pack.
The £300,000 capture from Rochdale forced in a Kris Commons' free-kick at the far post to put Forest ahead.
Oldham threatented to play their way back into the game before Holt set up Nathan Tyson for the former Wycombe striker to make it 2-0.
Holt sent Commons clear for a shot that Oldham keeper Chris Day pushed into the path of Nicky Southall, who rounded off Forest's best display of the season.
Nottm Forest: Gerrard, Perch, Bennett, Morgan, Breckin, Commons (Bastians 78), Thompson, Curtis (Gary Holt 70), Southall, Tyson, Grant Holt (Lester 86).
Subs Not Used: Bopp, Pedersen.
Booked: Bennett, Breckin.
Goals: Grant Holt 25, Tyson 63, Southall 67.
Oldham: Day, Branston, Haining (Scott 72), Swailes, Forbes (Hughes 70), Edwards, Grant, Wellens, Warne, Killen (Beckett 69), Liddell.
Subs Not Used: Cronin, Eyres.
Ref: S Dorr (Worcester).