UK light-heavyweight Buatsi made a winning yet underwhelming debut to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round bout at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the techniques didn't complement each other, with frequent clinching disrupting the fight.
Two judges scored it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest performance but how do champions respond? They prevail," the victor commented in the ring as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Several boxing experts felt the challenger, 31, deserved the win but the contender endured the second setback of his 28-fight professional journey.
The Champion Claims Triumph in Uneventful Affair
The fighter's advancement has slowed in recent years through management issues and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter willing to take risks in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a protective stance to edge the better periods.
The audience's tolerance decreased amid regular grabbing, with Parker falling to the floor multiple occasions during clinches.
The underdog ended stronger, but many rounds were challenging to assess. Nevertheless, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
Buatsi moves on, but with the presence of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Homage Fuels All-Manchester Battle
In the supporting bout, Arthur beat Bradley Rea by close verdict in a terrific all-Manchester fight to secure the European light-heavyweight belt.
The stadium grew hushed for a deeply poignant memorial prior to the bout as ten bells sounded in remembrance of the city's native Hatton, who passed away aged 46 in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound ended, the stillness transitioned to a shout of "only one Ricky Hatton".
The fighting within the ring matched the feeling. Arthur was sent to the canvas by a powerful punch flush on the chin in the early round, standing uncertainly to his feet on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, the opponent - in opposing blue - was injured soon, significant bruising appearing under his orbital area as the pair exchanged punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over 12 rounds.
Arthur barely secured the decision with official scores of draw, 115-113 and 115-112, but both fighters were persistent and courageous, everything their hero Hatton stood for.
