Cejudo, 31, a native of Los Angeles, took home the decision on judges' scores of 48-47 (twice), which was the same score the third judge had in favor of Johnson.
"Wherever [UFC president] Dana White is, I felt disrespected this whole time", Cejudo said.
Earlier in the evening, veteran Cub Swanson aims to get back in the win column after back-to-back losses as he battles Renato Moicano in a clash of featherweights as a +285 underdog, while middleweight Kevin Holland makes his UFC promotional debut, battling Thiago Santos, also as a +285 underdog.
With a decisive first-round knockout in the main event of UFC 227, TJ Dillashaw may have put his rivalry with Cody Garbrandt to rest, as he successfully defended his UFC bantamweight title for the first time with a second finish of his former training partner at Los Angeles' STAPLES Center. Demetrious Johnson didn't go up (to bantamweight).
"It wasn't anything in sparring", Dillashaw said. There is a very big card coming up in NY with numerous top guys from my division on it and I would like to join them. Before the opening frame closed, Cejudo briefly took Johnson down and also appeared to land a hard left.
Watch Tiger Woods Sink Ridiculous 50-Foot Putt At WGC-Bridgestone Invitational
If it does, imagine how high expectations will be for Woods at next week's PGA Championship. It's a very simple, straightforward golf course, which we don't see very often anymore.
"He's a very dominant champion", Dillashaw said.
Garbrandt continues fighting as round 1 is coming to a close, but the Team Alpha Male product did not look right. Another Dillashaw right - it landed more like a clothesline than a punch - had "No Love" teetering on the brink.
Dillashaw called Garbrandt's chin into question ahead of the rematch, but he held up well to the final onslaught.
The win definitely puts Dillashaw in an enviable position as the reigning and defending bantamweight champion after dispatching Garbrandt in back-to-back fights. He plays a unsafe game.
Cejudo won his first 10 pro fights to earn his first shot at Johnson, but Mighty Mouse stopped him with a flurry of punches in the first round of their first meeting 28 months ago. It was more when I hit him in the first fight with my foot.
And with back-to-back wins over "No Love", Dillashaw believes his rivalry with the OH native and TAM is now a thing of the past. "I wanted to beat his right hand with my own and show him who has the real power".