Font (15-3) dropped Almeida with a right hand early in the second frame and kept the pressure on after the Brazilian rose to his feet.
He hurt him again moments later with a head kick and follow-up right uppercuts for the TKO. The sensational finish brought the sellout crowd to its feet inside TD Garden.
Almeida (21-3) did everything he could to recover, including opening up with punches of his own to back Font off.
The early action was relatively balanced, as Almeida responded to Font's jab with leg kicks and a handful of rights hands. He caused a small cut under Font's left eye. Ultimately, however, he couldn't answer Font's pressure.
Font is 3-1 in his last four, while Almeida falls to 1-3 in his last four.
The Massachusetts native dropped Burgos with a flush right uppercut in the center of the cage, after Burgos came up short on a takedown attempt. Burgos got back to his feet but was badly wobbled and was dropped again moments later.
He was in the process of getting up again, when referee Dan Miragliotta stopped the bout.
Kattar improves to 2-0 in the UFC and has defeated two promising up-and-comers in Burgos and Andre Fili. His jab was especially on point Saturday and appeared to throw off Burgos' offense.
Burgos, of New York, is now 3-1 in the Octagon.
Villante edges Barroso with split-decision win
Two judges scored the contest 30-27 for Villante, while a third inexplicably saw it 29-28 for Barroso.
Villante, of New York, walked Barroso down from start to finish. His best work came along the fence, after he backed Barroso up.
Barroso landed a handful of solid counter left hands and ripped a couple kicks to the body, but it was otherwise a lackluster performance for the Brazilian. His overall UFC record now drops to 4-4.
Villante, 32, picks up his first win since December 2016.