UK light-heavyweight Buatsi made a winning yet disappointing debut to life under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a competitive 10-round fight at the boxing arena.
But Parker found success, delivering effective single shots in a fight where the styles never quite clicked, with excessive holding spoiling the contest.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi commented in the ringside as he was faced boos from the crowd.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Various analysts felt Parker, thirty-one, should have been awarded the victory but the British boxer endured the second defeat of his 28-bout career.
The Champion Claims Victory in Slow Affair
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of lack of fights.
Previously predicted as the future of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under fresh management.
He started carefully, with the two boxers prepared to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for Buatsi, who worked behind a protective stance to barely take the more effective rounds.
The spectators' acceptance wore thin during regular grabbing, with Parker falling to the floor various instances during clinches.
Parker ended stronger, but many rounds were difficult to score. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Homage Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a excellent all-Manchester contest to capture the European light heavyweight belt.
The stadium fell silent for a extremely emotional homage ahead of the contest as 10 bells tolled in honor of local hero Ricky Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime ended, the silence gave way to a chant of "there's just one Hatton".
The fighting during the bout equaled the feeling. Arthur was sent to the canvas by a significant blow directly to the chin in the early round, rising shakily to his feet on the count of eight.
But the traditional red equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in opposing blue - was damaged quickly, heavy swelling forming under his orbital area as the pair landed punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over 12 rounds.
Arthur edged the decision with judges scorecards of 114-114, 115-113 and wider gap, but each competitor were persistent and brave, everything their idol the legend embodied.
