British light-heavyweight Buatsi secured a victory yet disappointing debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close 10-round bout at the Manchester venue.
But the challenger landed significant shots, delivering effective clean blows in a match where the approaches didn't complement each other, with excessive holding marring the contest.
Two judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They win," the victor stated in the arena as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Several boxing experts believed Parker, thirty-one, deserved the win but the contender endured the second loss of his 28-match career.
The Champion Claims Triumph in Uneventful Match
The fighter's advancement has stalled in recent times through contract problems and considerable time of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under recent support.
He started carefully, with the two boxers prepared to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to narrowly win the better stanzas.
The crowd's patience wore thin during regular grabbing, with the challenger going down several times during grappling.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Homage Inspires Manchester Derby Contest
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a terrific local rivalry battle to win the European light heavyweight belt.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as ten bells sounded in memory of local hero Hatton, who passed away aged 46 in recently.
It was the first major televised match card in the urban center since Hatton's death. As the last bell faded, the silence became a chant of "there's only one Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was floored by a significant blow directly to the chin in the initial stage, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, the opponent - in rival City blue - was damaged quickly, significant bruising forming under his orbital area as the duo landed powerful shots.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the intensity rarely dropped over 12 rounds.
Arthur edged the result with official scores of 114-114, narrow lead and wider gap, but both fighters were persistent and brave, all the qualities their inspiration Hatton embodied.
