UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a majority decision in a close 10-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful clean blows in a match where the styles failed to mesh, with constant grabbing disrupting the fight.
The officials judged it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi stated in the ring as he was met by boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the decision but the British boxer endured the second loss of his 28-fight professional journey.
The Champion Secures Triumph in Dull Encounter
His career development has stalled in recent years through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to realize his potential - maybe in what appears to be a last chance - under recent support.
He started carefully, with the two boxers ready to overcommit in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who utilized a solid defense to edge the more effective periods.
The spectators' acceptance decreased during constant clinching, with the challenger falling to the floor several times during clinches.
Parker closed well, but multiple periods were challenging to assess. However, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter David Benavidez, and Russian champion Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Fight
In the secondary fight, Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester battle to secure the European light heavyweight title.
The stadium fell silent for a deeply poignant homage prior to the bout as 10 bells tolled in memory of Manchester's own Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound faded, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The fighting inside the ropes equaled the feeling. Arthur was floored by a left hook directly to the jaw in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red attire of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up early, noticeable damage forming under his face as the duo traded hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the decision with official scores of 114-114, narrow lead and wider gap, but the two athletes were determined and full of heart, exactly what their idol Hatton represented.
