UK light heavyweight Buatsi made a winning yet unimpressive start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a fight where the styles didn't complement each other, with constant grabbing marring the action.
The officials had it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my finest showing but what defines champions? They prevail," the victor stated in the ringside as he was greeted with negative reactions from the crowd.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the British boxer suffered the second setback of his 28-fight career.
The Champion Claims Win in Uneventful Match
Buatsi's progress has stalled in recent years through management issues and extended periods of lack of fights.
Once tipped as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a last chance - under new promotional backing.
He began cautiously, with the two boxers ready to overcommit in a calculated early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for the favorite, who utilized a protective stance to narrowly win the more effective stanzas.
The crowd's patience wore thin amid frequent holding, with Parker going down multiple occasions during clinches.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Homage Inspires Manchester Derby Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester battle to win the continental championship.
The venue became quiet for a deeply poignant homage before the fight as 10 bells rang in memory of Manchester's own Hatton, who succumbed aged 46 in September.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the last bell faded, the silence gave way to a chant of "there's only one Ricky Hatton".
The action inside the ropes reflected the feeling. Arthur was knocked down by a significant blow directly to the jaw in the second round, standing uncertainly to his position on the count of eight.
But the traditional red shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was marked up soon, noticeable damage developing under his orbital area as the pair traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor narrowly won the decision with official scores of even score, close margin and wider gap, but each competitor were determined and brave, exactly what their hero the legend represented.
