British light heavyweight Buatsi earned a win yet unimpressive debut to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a tight ten-round contest at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a match where the techniques never quite clicked, with frequent clinching disrupting the contest.
Two judges scored it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They succeed," Buatsi said in the ringside as he was greeted with negative reactions from the audience.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a 20th career victory.
Various analysts believed Parker, 31, merited the win but the contender suffered the second loss of his 28-match professional journey.
The Champion Secures Triumph in Uneventful Affair
The fighter's advancement has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors willing to take risks in a cagey opening few rounds.
Parker, whose sole prior loss 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, Parker had stayed in contention, making life awkward for the favorite, who utilized a solid defense to edge the more effective periods.
The crowd's patience diminished during constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker ended stronger, but many rounds were hard to judge. Although, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the supporting bout, Arthur beat Rea by split-decision in a excellent local rivalry battle to secure the European light heavyweight belt.
The arena grew hushed for a profoundly moving tribute prior to the bout as a bell ceremony tolled in memory of the city's native Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the last bell ended, the silence gave way to a chant of "there's just one Hatton".
The competition within the ring matched the feeling. The eventual winner was knocked down by a powerful punch squarely on the face in the early round, standing uncertainly to his feet on the eight count.
But the traditional red attire of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was damaged early, significant bruising developing under his face as the pair landed punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
Arthur edged the result with scoring tallies of even score, narrow lead and wider gap, but both fighters were persistent and full of heart, exactly what their inspiration the legend embodied.
