Jesse Were scored from the spot to help Zesco United consolidate their lead at the top of Zambian Super League with only three matches to go.
Were and his Zesco United compatriots now require only a win in their remaining three games to wrap up the Zambian title they surrendered last season.
Zesco United forward John Ching'andu was brought down in the box early in the second half and the Harambee Stars forward stepped up at the Levy Mwanawasa Stadium to restore Zesco United's advantage.
Forest Rangers had leveled scores from the penalty spot through Logic Ching'andu while Zesco United had taken a deserved lead via Fackson Kopombe's goal in the 12th minute.
Zesco United are top of the log with 69 points after 35 rounds of matches, five above second-placed Zanaco.