UK light heavyweight Buatsi secured a victory yet unimpressive start to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a close ten-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a fight where the approaches failed to mesh, with excessive holding disrupting the contest.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my best showing but what do champions do? They prevail," Buatsi stated in the ring as he was faced boos from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Encounter
His career development has plateaued in recent times through contract problems and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now is positioned trying to realize his potential - possibly in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter prepared to be aggressive in a tentative initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to edge the more effective stanzas.
The spectators' acceptance diminished during regular grabbing, with Parker going down various instances during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. However, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, giving Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Inspires Manchester Derby Contest
In the supporting bout, Arthur beat Rea by split-decision in a excellent local rivalry contest to secure the European light heavyweight belt.
The venue became quiet for a profoundly moving memorial prior to the bout as ten bells tolled in memory of the city's native Hatton, who passed away aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the last bell ended, the quiet became a shout of "only one Ricky Hatton".
The competition during the bout matched the feeling. The eventual winner was knocked down by a significant blow squarely on the chin in the second round, rising shakily to his feet on the referee's count.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured quickly, heavy swelling developing under his orbital area as the fighters exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur edged the decision with official scores of draw, close margin and 115-112, but each competitor were determined and brave, all the qualities their inspiration Hatton represented.
