UK light-heavyweight Buatsi secured a victory yet underwhelming start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a majority decision in a competitive 10-round contest at the boxing arena.
But Parker landed significant shots, landing some telling single shots in a fight where the styles never quite clicked, with constant grabbing spoiling the action.
The officials had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest showing but what defines champions? They win," Buatsi commented in the ring as he was greeted with boos from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Various analysts felt the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter experienced the second loss of his 28-bout professional journey.
The Champion Secures Victory in Dull Match
His career development has plateaued in recent years through contract problems and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He opened tentatively, with both competitors ready to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who utilized a solid defense to barely take the cleaner rounds.
The audience's tolerance decreased during regular grabbing, with the challenger slipping to the canvas various instances during clinches.
The underdog finished the stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a excellent all-Manchester fight to win the European light-heavyweight belt.
The arena became quiet for a deeply poignant homage before the fight as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who died at age 46 in last month.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound faded, the silence transitioned to a shout of "only one Hatton".
The action within the ring reflected the sentiment. The eventual winner was sent to the canvas by a powerful punch squarely on the chin in the second round, rising shakily to his feet on the referee's count.
But the traditional red shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was marked up quickly, heavy swelling forming under his face as the pair landed punishing blows.
The challenger, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
The victor barely secured the verdict with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were relentless and brave, all the qualities their idol Hatton represented.
