Jake Paul Beats Julio Cesar Chavez Jr. By Unanimous Decision

Jake Paul just took down another former boxing champ ... defeating Julio Cesar Chavez Jr. by unanimous decision on Saturday.

The crowd at the Honda Center in Anaheim was overwhelmingly in support of 39-year-old Chavez Jr -- but for the most part, they didn't get the show they were hoping for.

The early rounds easily belonged to 28-year-old Paul ... with Chavez Jr. hardly throwing -- let alone landing -- any punches, to the point where the fans started to voice their disproval.

Paul -- who last beat Mike Tyson in November -- did his best to get Chavez Jr. involved ... and landed some solid shots in the process, but got no response.

The announcers criticized Chavez Jr. -- who earned the WBC middleweight title in 2011 -- for his low energy performance out the gates ... even pointing out how he was complaining to the ref more than fighting.

Chavez Jr.'s issues stemmed from shots he felt were to the back of the head and below the belt ... but the ref didn't see it that way.

The sixth round got the crowd back into it -- Chavez Jr. looked like an entirely different fighter. He landed clean looks on Paul ... who was forced to tie up with his opponent.

Chavez Jr. had control in the final two rounds ... and Paul's efforts up to that point appeared to finally catch up to him as he took a beating.

As the broadcast pointed out, Chavez Jr. (54-6-1) landed just over 60 punches in the bout ... but the majority came in the final rounds

After the final bell, it went to the judges' scorecards -- 99-91, 97-93, 98-92 -- with Paul's hand being raised, earning him his 12th career victory.

Paul (now 12-1) had some words for the spectators present following their boo birds ... telling them to "shut the f*** up."

He also took a moment to send a prayer for his former opponent Ben Askren -- adding he and Logan will be donating to a fundraiser to help pay his medical bills as he battles severe pneumonia.