British light heavyweight Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight ten-round fight at the boxing arena.
But the challenger found success, landing some telling clean blows in a match where the styles never quite clicked, with constant grabbing disrupting the fight.
Two judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but what defines champions? They win," the victor stated in the ringside as he was greeted with boos from the spectators.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a 20th pro success.
Several boxing experts believed the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second loss of his 28-fight career.
The Champion Secures Victory in Uneventful Match
Buatsi's progress has slowed in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second bout at the higher weight class.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who operated with a solid defense to barely take the better rounds.
The crowd's patience wore thin during frequent holding, with the challenger slipping to the canvas various instances during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Inspires Local Rivalry Battle
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a outstanding all-Manchester battle to win the European light heavyweight belt.
The arena fell silent for a extremely emotional tribute ahead of the contest as ten bells tolled in memory of local hero Ricky Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime faded, the silence became a roar of "only one Ricky Hatton".
The action within the ring matched the sentiment. Arthur was floored by a powerful punch directly to the chin in the early round, standing uncertainly to his feet on the eight count.
But the Manchester United-red attire of the fighter soon advanced again. From the other corner, Rea - in rival City blue - was damaged quickly, noticeable damage forming under his eye as the pair exchanged punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
The victor barely secured the result with scoring tallies of 114-114, 115-113 and wider gap, but the two athletes were relentless and courageous, everything their idol Hatton represented.
