British light-heavyweight Buatsi earned a win yet underwhelming beginning 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 judges' verdict in a tight 10-round bout at the boxing arena.
But Parker found success, landing some telling individual punches in a fight where the approaches failed to mesh, with excessive holding spoiling the action.
Two judges had it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest display but what defines champions? They succeed," Buatsi stated in the arena as he was greeted with negative reactions from the spectators.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to secure a 20th career victory.
Several boxing experts felt the challenger, 31, merited the victory but the British boxer endured the second loss of his 28-bout career.
Buatsi Earns Victory in Dull Match
His career development has plateaued in the past few years through management issues and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to achieve expectations - perhaps in what appears to be a last chance - under recent support.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after breaking his hand during the bout, was making just his second bout at light-heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for Buatsi, who operated with a solid defense to barely take the more effective periods.
The crowd's patience wore thin amid regular grabbing, with the challenger going down several times during close exchanges.
Parker ended stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - 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 Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to win the European light heavyweight championship.
The arena grew hushed for a profoundly moving tribute ahead of the contest as 10 bells sounded in memory of the city's native Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the final chime disappeared, the quiet became a shout of "only one Hatton".
The fighting inside the ropes reflected the feeling. Arthur was sent to the canvas by a left hook directly to the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of the fighter soon came forward again. Across the ring, Rea - in rival City blue - was marked up quickly, significant bruising forming under his eye as the duo exchanged powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the action hardly diminished over the full distance.
The victor edged the verdict with official scores of draw, narrow lead and wider gap, but each competitor were determined and full of heart, all the qualities their idol Hatton represented.
