British light-heavyweight Buatsi earned a win yet unimpressive debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a tight ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling clean blows in a fight where the techniques failed to mesh, with excessive holding marring the action.
The officials scored it 96-94 for to the winner, with the final judge a even score.
"It wasn't my finest performance but how do champions respond? They succeed," Buatsi stated in the ring as he was met by boos from the crowd.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought the challenger, thirty-one, deserved the victory but the British boxer endured the second loss of his 28-fight professional journey.
Buatsi Secures Triumph in Dull Encounter
The fighter's advancement has slowed in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast 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 final roll of the dice - under recent support.
He started carefully, with neither fighter willing to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after breaking his hand during the bout, was participating in his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, causing problems for the favorite, who utilized a protective stance to edge the more effective stanzas.
The crowd's patience wore thin because of regular grabbing, with Parker falling to the floor various instances during grappling.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the co-main event, Arthur beat Bradley Rea by close verdict in a terrific local rivalry battle to secure the continental championship.
The stadium fell silent for a extremely emotional memorial ahead of the contest as a bell ceremony sounded in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the final chime disappeared, the quiet transitioned to a shout of "there's only one Ricky Hatton".
The competition within the ring matched the feeling. Arthur was floored by a left hook directly to the chin in the early round, rising shakily to his feet on the count of eight.
But the traditional red attire of Arthur soon advanced again. On the opposite side, Rea - in opposing blue - was injured early, noticeable damage appearing under his orbital area as the fighters landed punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
Arthur barely secured the verdict with official scores of 114-114, narrow lead and clearer margin, but the two athletes were relentless and brave, everything their inspiration Hatton represented.
