UK light-heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a close 10-round contest at the boxing arena.
But the challenger found success, landing some telling clean blows in a match where the styles never quite clicked, with frequent clinching spoiling the fight.
The officials scored it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my greatest performance but what do champions do? They win," the victor commented in the arena as he was met by negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second defeat of his 28-fight career.
Buatsi Claims Victory in Dull Encounter
His career development has slowed in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to realize his potential - possibly in what feels like a ultimate opportunity - under recent support.
He began cautiously, with both competitors willing to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was making just his second bout at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a tight guard to narrowly win the cleaner periods.
The audience's tolerance wore thin amid regular grabbing, with Parker falling to the floor various instances during close exchanges.
Parker closed well, but several stanzas were challenging to assess. However, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Contest
In the supporting bout, Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester battle to secure the European light-heavyweight belt.
The stadium fell silent for a deeply poignant homage prior to the bout as a bell ceremony sounded in remembrance of local hero Hatton, who died at age 46 in recently.
It was the premier televised fight night in the city since Hatton's passing. As the concluding sound disappeared, the silence transitioned to a shout of "only one Hatton".
The fighting within the ring reflected the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the face in the second round, standing uncertainly to his footing on the count of eight.
But the red-colored attire of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was injured soon, noticeable damage developing under his eye as the pair exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur narrowly won the verdict with judges scorecards of 114-114, narrow lead and clearer margin, but the two athletes were determined and full of heart, exactly what their idol Hatton stood for.
