British light heavyweight Buatsi earned a win yet disappointing beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight 10-round contest at the boxing arena.
But the challenger landed significant shots, delivering effective single shots in a contest where the styles didn't complement each other, with excessive holding disrupting the action.
Two judges had it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but what do champions do? They win," the victor stated in the ringside as he was greeted with boos from the spectators.
The Londoner bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Several boxing experts thought the challenger, thirty-one, merited the decision but the British boxer suffered the second setback of his 28-bout professional journey.
The Champion Earns Win in Dull Match
Buatsi's progress has plateaued in recent times through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a last chance - under new promotional backing.
He started carefully, with the two boxers ready to be aggressive in a cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after damaging his hand mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who worked behind a solid defense to barely take the cleaner stanzas.
The audience's tolerance decreased amid regular grabbing, with Parker falling to the floor multiple occasions during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Inspires Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester fight to win the European light heavyweight belt.
The stadium grew hushed for a profoundly moving homage before the fight as a bell ceremony rang in memory of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised match card in the location since Hatton's passing. As the last bell faded, the quiet became a roar of "there's only one Hatton".
The competition inside the ropes equaled the feeling. The eventual winner was knocked down by a significant blow flush on the chin in the second round, rising shakily to his footing on the referee's count.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged quickly, significant bruising appearing under his face as the duo traded powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of even score, close margin and clearer margin, but each competitor were persistent and full of heart, exactly what their idol the legend embodied.
