Dumont (6-1-0) replaced the injured Danyelle Wolf on the card at the UFC's Apex production facility.
It marked the first outing for the Montreal-born Spencer (8-3-0), who now calls Orlando home, since last June when she lost a decision to featherweight champion Amanda (Lioness) Nunes at UFC 250.
Dumont was coming off a decision win over Ashlee Evans-Smith in November. She lost her UFC debut to Megan Anderson in February 2020.
It was a cagey opening with Spencer looking to be the aggressor, often leading with leg kicks, while Dumont looked to counter-punch. The two clinched at the fence late in a close first round with Dumont scoring with a nice knee.