British light-heavyweight Buatsi earned a win yet underwhelming beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a tight ten-round bout at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a fight where the styles failed to mesh, with frequent clinching spoiling the contest.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They win," Buatsi said in the arena as he was met by boos from the spectators.
The British fighter got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers believed Parker, thirty-one, merited the decision but the contender suffered the second loss of his 28-bout career.
Buatsi Earns Win in Dull Encounter
The fighter's advancement has stalled in recent years through management issues and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to barely take the more effective periods.
The crowd's patience decreased because of frequent holding, with Parker slipping to the canvas several times during grappling.
Parker finished the stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Motivates Local Rivalry Fight
In the secondary fight, Arthur beat Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to capture the European light heavyweight title.
The stadium grew hushed for a extremely emotional memorial ahead of the contest as ten bells tolled in memory of Manchester's own Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the concluding sound ended, the silence gave way to a roar of "there's only one Hatton".
The fighting within the ring reflected the feeling. The eventual winner was floored by a left hook squarely on the face in the second round, standing uncertainly to his footing on the referee's count.
But the traditional red equipment of the fighter soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured quickly, noticeable damage forming under his eye as the duo traded hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur edged the result with official scores of 114-114, narrow lead and clearer margin, but each competitor were determined and brave, exactly what their idol Hatton represented.
