
Substitute Hermenegildo 'Geraldo' Bartolomeu levelled for the hosts in the 90th minute and Muselenge 'Bobo' Ungenda won the match with a goal eight minutes into stoppage time.
John Ching'andu had put 2016 Champions League semi-finalists Zesco ahead on 67 minutes at the 50,000-capacity national stadium in the Angolan capital.
Ungenda was one of two Democratic Republic of Congo footballers in the Primeiro starting line-up and there were also a couple of Nigerians.
Victory lifted Primeiro from last to second in the four-club Group D, greatly enhancing their chances of finishing runners-up to probable table-toppers Etoile Sahel of Tunisia.
Former African champions Etoile have home advantage over Mbabane Swallows of eSwatini (formerly Swaziland) later Friday and are expected to win and seal a quarter-finals spot.
Etoile, the only winners of all five current and past CAF club competitions, have seven points, Primeiro five, Swallows four and Zesco two.
AFP