The Stags continued to struggle after that, with only Hawke's Bay's Brad Schmulian (68 not out) able to the hold the line, but eventually running out of partners, as his side was dismissed for 254 inside of 74 overs.
Needing only 53 runs for victory, the Firebirds had wrapped up their run chase in just the 17th over, although they did lose Fraser Colson caught behind to give Nelson's Willem Ludick his fourth wicket of the match.
However, Rachin Ravindra and Devon Conway ticked off the remaining 31 runs required for victory in brisk order for the easy win.
This season's introduction of a new style of Kookaburra ball, with an extra layer of lacquer, saw late swing come into play at a green Basin Reserve, which led to the Stags woes on Day 1 from which they couldn't recover.
The Firebirds win saw them move 13 points clear at the top of the points table.