NBA star Donovan Mitchell says the refs straight-up "screwed" the Utah Jazz out of a win Wednesday night against the 76ers ... slamming the officiating as "f**king ridiculous."

The All-Star guard was booted from the game in the final minute of the Jazz's 131-123 loss to Philadelphia in OT ... after receiving two technical fouls for arguing with refs over calls.

Mitchell was LIVID as he headed to the locker room ... unleashing his frustrations on a nearby water cooler as he left the court.

After the game, Mitchell continued to blast the refs ... saying, "It's tough to go out there and see how we fight and compete, and to have a game like that taken from us."

"This whole refereeing stuff ... We're nice, we don't complain, like, we don't get frustrated, we fight through things, and the fact that we continually get ... screwed, in a way, by this. You know?”

Spida -- an MVP candidate for the Western Conference-leading Jazz -- had a fantastic game leading up to the ejection with 33 points, 8 rebounds and 6 assists ... and feels the Jazz should have gone home with the W.

"We won this game, in my personal opinion," Mitchell said. "But like I said, I’m going to give them credit. They won. Whatever. Cool."

"But it’s been a consistent thing, and the question is, ‘Can we do it? Can we sustain it? Are we for real #1? And, yeah, the hell we are. And it’s getting f**king ridiculous that this is what is happening."

Jazz big man Rudy Gobert had Mitchell's back after the game ... telling the media he hopes the refs are embarrassed by their performance.

"I think it's disrespectful, to be honest, to the game of basketball and to our team, and hopefully, they're going to watch the game when they get home," Gobert said.

"Hopefully, they feel ashamed when they watch the game."

It’s a good bet Mitchell and Gobert can expect a letter in the mail from the league in the near future.