"I think this judge needs to be investigated," Gilbert told TMZ Sports, adding, "We need the FBI on this judge. Those judge might be working with the betting company."

If you missed it, 30-year-old Sandhagen (ranked 5th before the fight) and 30-year-old Vera (ranked 3rd) fought in the main event at UFC Fight Night on Saturday night in San Antonio ... a 5-round scrap that went to the judge's scorecards.

After the fight, both men stood at the center of the Octagon, as Bruce Buffer announced a "split decision" ... and, cue the head-scratching.

Judge Sal D'Amato scored the fight 50-45 for Cory (5 rounds to none), while Chris Lee scored it 49-46 (4 rounds to 1 for Sandhagen). But, Ojeda, was seemingly watching another fight ... scoring the bout 48-47 for Chito (3 rounds to 2).

D'Amato and Lee have loads of experience, while Ojeda has worked only a handful of UFC fights (4).

Now, Chito is one of the baddest dudes in the world, but Saturday just wasn't his night ... by just about every metric.

"Chito's my guy and I want him to win, but, theres no way he won that fight," Burns said. "It's clear to anyone. What's wrong with that judge?"

Further proof ... according to the UFC's official stats, Chito landed 73 strikes to Cory's 187. Sandhagen was also credited with 3 takedowns, resulting in over 7 minutes of control time. Vera attempted 1 takedown but was unsuccessful.

Even Dana was floored.

“I was literally coming out of the bathroom and I was like, ‘What the f**k?’”

The UFC honcho continued ... "It could have been 5-0, it could have been [4 rounds to 1], but [split decision]? Wow, that’s pretty scary.”

We reached out to the Texas Dept. of Licensing & Regulation, who oversee judges in the state, and they told us "TDLR is aware of the concerns about the scoring in one of Saturday's UFC fights. All TDLR officials receive ongoing training and we monitor each fight for consistency and accuracy in scoring."

When we followed up, questioning whether the judge was being investigated, TDLR said they couldn't comment on individual judges, but added they review performance after each event.

We also talked to Gilbert about his upcoming UFC 287 co-main fight with rival Jorge Masvidal ... a fight he says he's gunning to win by knockout our finish 'cause -- can't trust the scoring!