British light heavyweight Buatsi made a winning yet underwhelming debut to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight 10-round fight at the boxing arena.
But the challenger landed significant shots, connecting with powerful single shots in a contest where the approaches failed to mesh, with constant grabbing spoiling the contest.
The officials scored it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," Buatsi said in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts believed Parker, 31, should have been awarded the win but the Derbyshire fighter endured the second setback of his 28-match professional journey.
Buatsi Earns Win in Slow Affair
Buatsi's progress has stalled in the past few years through management issues and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a tight guard to narrowly win the better periods.
The spectators' acceptance decreased during regular grabbing, with Parker falling to the floor various instances during close exchanges.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Hatton Homage Fuels Local Rivalry Battle
In the secondary fight, Arthur beat Rea by close verdict in a excellent Manchester vs Manchester fight to secure the European light heavyweight title.
The venue grew hushed for a deeply poignant homage prior to the bout as 10 bells tolled in remembrance of local hero Ricky Hatton, who succumbed 46 years old in September.
It was the first major televised fight night in the location since the passing of Hatton. As the final chime faded, the silence transitioned to a chant of "there's only one Ricky Hatton".
The action inside the ropes reflected the emotion. Arthur was knocked down by a left hook squarely on the jaw in the initial stage, rising shakily to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. On the opposite side, Rea - in competitive blue - was damaged soon, significant bruising appearing under his orbital area as the duo landed hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the intensity rarely dropped over the full distance.
The victor barely secured the verdict with judges scorecards of 114-114, narrow lead and clearer margin, but the two athletes were relentless and brave, everything their inspiration Hatton stood for.
