UK light-heavyweight Buatsi earned a win yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close 10-round contest at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a match where the approaches never quite clicked, with constant grabbing disrupting the action.
The scoring judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi said in the ringside as he was faced boos from the spectators.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers thought Parker, thirty-one, should have been awarded the decision but the British boxer experienced the second defeat of his 28-match professional journey.
The Champion Secures Victory in Slow Match
His career development has stalled in recent years through contract problems and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under fresh management.
He opened tentatively, with the two boxers willing to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to edge the more effective rounds.
The spectators' acceptance wore thin because of constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but many rounds were challenging to assess. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a excellent local rivalry fight to capture the European light heavyweight belt.
The arena became quiet for a extremely emotional tribute before the fight as ten bells sounded in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised match card in the city since the passing of Hatton. As the concluding sound faded, the stillness gave way to a shout of "there's only one Hatton".
The competition inside the ropes matched the feeling. Arthur was floored by a significant blow directly to the chin in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was injured quickly, noticeable damage developing under his eye as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the result with scoring tallies of draw, close margin and wider gap, but both fighters were relentless and brave, all the qualities their idol Hatton embodied.
