British light-heavyweight Buatsi made a winning yet disappointing beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive ten-round fight at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a contest where the approaches failed to mesh, with frequent clinching disrupting the contest.
The scoring judges had it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They win," the victor commented in the ring as he was faced negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts believed Parker, thirty-one, merited the win but the contender experienced the second loss of his 28-match professional journey.
The Champion Earns Victory in Uneventful Match
Buatsi's progress has stalled in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the future of British boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors prepared to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second fight at the higher weight class.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who utilized a protective stance to barely take the better stanzas.
The audience's tolerance diminished amid constant clinching, with Parker slipping to the canvas several times during clinches.
The underdog closed well, but several stanzas were challenging to assess. However, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Homage Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a terrific all-Manchester fight to secure the European light heavyweight championship.
The stadium fell silent for a deeply poignant tribute ahead of the contest as a bell ceremony tolled in honor of the city's native Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the concluding sound ended, the stillness became a chant of "only one Ricky Hatton".
The fighting during the bout matched the feeling. The eventual winner was floored by a significant blow squarely on the face in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was injured early, significant bruising forming under his orbital area as the fighters traded powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur narrowly won the decision with scoring tallies of draw, 115-113 and wider gap, but both fighters were determined and courageous, all the qualities their hero the legend represented.
