In a game played across six 15-minute intervals, Liam Cross and Sam Hoskins were on target for a youthful Northampton squad, which featured 16-year-old academy player Josh Tomlinson. New signings Danny Hylton, Ben Fox and Ryan Haynes were also involved.
Louis Appere had an early shot blocked before the same player was denied again having been played in by strike partner Hylton. Haynes then fired over from distance as the first 15 minutes drew to a close.
Max Dyche was fouled to give the Cobblers a penalty at the start of the second period, but Hylton saw his spot-kick saved.
The Cobblers took the lead early in the third period, Liam Cross curling home from the edge of the area, before Miguel Ngwa and Hylton both went close.
Substitute keeper Jonny Maxted made a good save at the start of the fourth period but Forest were soon level, a deflected effort finding the net, however Cobblers quickly restored their lead, Cross was tripped in the area and Sam Hoskins converted from the penalty spot.
Hoskins was then wide from distance as the first pre-season work out for Jon Brady's side drew to a close.
The Cobblers head north to their week long Scottish training camp on Monday.