The match also marked a winning start for Zesco’s new coach Zlatko Krmpotic who replaced George Lwandamina few weeks ago, following the latter's decision to join Young Africans of Tanzania just months after guiding the Zambian club to the 2016 CAF Champions League semi-finals.
Zesco controlled the first half and could have been up by at least three goals heading into the break.
Striker Jesse Were sent his second minute header wide as Zesco pinned Ngozi on the ropes.
Ally Fatak had Ngozi's best chance in the period when his goalbound effort came off Anthony Akumu in the 12th minute.
Idris Mbombo then wasted great chances in the 14th and 18th minutes with the first saved and second parried by Ngozi goalkeeper Dieudonne Ntibahezwa.
The deadlock was broken in the 32nd minute when Mwanza beat his marker Lewis Vyizigiro to finally breach Ntibahezwa and send Zesco 1-0 into the break.
Zesco continued to dominate Ngozi and had the ball in the back of the net in the 64th minute through Mbombo but referee Norman Matemera ruled it out for offside.
However, nine minutes later, Zesco got it right when Mtonga blasted from close-range a John Chingandu corner that was initially flapped into his path by Ntibahezwa.
The two sides meet in the final leg on March 18 in Bujumbura.