British light heavyweight Buatsi earned a win yet underwhelming start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a close 10-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a fight where the approaches didn't complement each other, with frequent clinching marring the fight.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They win," Buatsi stated in the ring as he was faced negative reactions from the audience.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Several boxing experts felt the challenger, 31, should have been awarded the victory but the British boxer endured the second loss of his 28-bout career.
Buatsi Secures Win in Dull Encounter
The fighter's advancement has slowed in recent years through management issues and extended periods of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter prepared to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to narrowly win the cleaner periods.
The crowd's patience wore thin because of constant clinching, with the challenger going down several times during grappling.
The underdog ended stronger, but multiple periods were hard to judge. Although, ex-champion Carl Frampton - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
The victor advances, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a terrific local rivalry battle to win the European light-heavyweight title.
The stadium grew hushed for a deeply poignant homage prior to the bout as ten bells tolled in honor of Manchester's own Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the last bell disappeared, the silence transitioned to a chant of "there's just one Ricky Hatton".
The fighting within the ring equaled the emotion. Arthur was knocked down by a powerful punch squarely on the face in the early round, rising shakily to his footing on the eight count.
But the traditional red equipment of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was injured quickly, noticeable damage appearing under his orbital area as the duo traded punishing blows.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
The victor barely secured the verdict with scoring tallies of 114-114, close margin and clearer margin, but each competitor were persistent and brave, all the qualities their hero Hatton embodied.
