British light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a tight ten-round bout at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful clean blows in a contest where the styles didn't complement each other, with excessive holding spoiling the contest.
The officials had it 96-94 to the winner, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They prevail," the victor said in the arena as he was met by negative reactions from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in February - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, merited the win but the contender experienced the second setback of his 28-fight professional journey.
Buatsi Secures Triumph in Slow Encounter
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what feels like a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a cagey early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the better rounds.
The spectators' acceptance diminished amid constant clinching, with the challenger slipping to the canvas various instances during grappling.
Parker ended stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the caliber of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Arthur defeated Bradley Rea by divided decision in a excellent local rivalry battle to capture the continental belt.
The venue grew hushed for a deeply poignant homage prior to the bout as a bell ceremony rang in memory of Manchester's own Ricky Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the city since the passing of Hatton. As the last bell faded, the stillness became a shout of "there's just one Ricky Hatton".
The competition during the bout equaled the emotion. Arthur was knocked down by a powerful punch directly to the chin in the second round, rising shakily to his footing on the count of eight.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was damaged quickly, heavy swelling forming under his eye as the duo traded hard punches.
Rea, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
Arthur barely secured the verdict with scoring tallies of draw, close margin and 115-112, but both fighters were relentless and full of heart, everything their inspiration Hatton stood for.
