The 26-year-old, on loan from Juventus, came forward in injury time and headed in Danilo Cataldi’s free-kick to earn his side a 2-2 draw and end a record-breaking run of 14 defeats.
Roberto De Zerbi’s side remain well adrift at the foot of the Serie A table and face a season-long battle to avoid relegation.
However for Brignoli it was all about that one moment and he confessed that he could see the goal coming just before it actually went in.
“When I was about to enter [Milan’s] box, the goal I would score flashed before me, 10 seconds before I scored,” he said. “It was like I was playing on a PlayStation. I saw it first in my head and then it came off.
“I didn’t even see the ball go in because I was looking in the opposite direction. I scored with the back of my head.”
Watford boss Javi Gracia does not think Abdoulaye Doucoure's form will be affected by his omission from France's latest squad.