British light heavyweight Buatsi made a winning yet disappointing debut to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a close 10-round bout at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a contest where the styles never quite clicked, with excessive holding spoiling the action.
The officials judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi said in the arena as he was greeted with boos from the audience.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Various analysts believed the challenger, 31, should have been awarded the decision but the British boxer experienced the second loss of his 28-bout professional journey.
The Champion Earns Victory in Uneventful Match
His career development has stalled in the past few years through contract problems and considerable time of inactivity.
Once tipped as the next star of British boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter ready to overcommit in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for the favorite, who utilized a protective stance to barely take the more effective periods.
The spectators' acceptance diminished during regular grabbing, with the challenger going down several times during grappling.
Parker finished the stronger, but many rounds were hard to judge. Although, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Fuels Manchester Derby Contest
In the supporting bout, Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester battle to win the European light-heavyweight championship.
The stadium became quiet for a profoundly moving memorial before the fight as ten bells sounded in honor of local hero Ricky Hatton, who passed away 46 years old in September.
It was the first major televised fight night in the city since Hatton's death. As the last bell faded, the stillness became a roar of "only one Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a powerful punch flush on the face in the early round, standing uncertainly to his feet on the count of eight.
But the traditional red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up early, heavy swelling forming under his orbital area as the duo traded hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with effective uppercuts as the action rarely dropped over the full distance.
The victor edged the decision with judges scorecards of even score, close margin and wider gap, but both fighters were determined and full of heart, all the qualities their hero the legend represented.
