British light heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a majority decision in a tight ten-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling single shots in a match where the approaches failed to mesh, with excessive holding disrupting the contest.
Two judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest showing but what defines champions? They win," the victor commented in the arena as he was greeted with boos from the crowd.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th career victory.
Various analysts believed Parker, thirty-one, merited the decision but the contender experienced the second loss of his 28-match career.
The Champion Earns Win in Slow Encounter
The fighter's advancement has stalled in recent years through promotional disputes and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to achieve expectations - possibly in what feels like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter willing to take risks in a tentative opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to edge the more effective rounds.
The crowd's patience wore thin during regular grabbing, with Parker going down various instances during clinches.
Parker closed well, but several stanzas were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just one round.
The victor progresses, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Motivates All-Manchester Contest
In the co-main event, Arthur overcame Rea by divided decision in a excellent local rivalry contest to capture the continental belt.
The stadium became quiet for a profoundly moving memorial before the fight as ten bells tolled in memory of Manchester's own Hatton, who died 46 years old in recently.
It was the premier televised fight night in the location since Hatton's death. As the concluding sound faded, the stillness became a shout of "only one Ricky Hatton".
The fighting within the ring equaled the feeling. Arthur was sent to the canvas by a powerful punch squarely on the jaw in the initial stage, getting up unsteadily to his position on the count of eight.
But the red-colored attire of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged early, significant bruising developing under his orbital area as the duo traded powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
Arthur narrowly won the verdict with official scores of draw, close margin and 115-112, but the two athletes were relentless and courageous, all the qualities their hero the legend stood for.
