UK light-heavyweight Buatsi made a winning yet unimpressive beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a close 10-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a match where the styles failed to mesh, with frequent clinching spoiling the fight.
The officials scored it 96-94 to the winner, with the third a even score.
"It wasn't my best showing but how do champions respond? They win," Buatsi said in the arena as he was greeted with boos from the spectators.
The British fighter got back to winning after his first professional defeat - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Some ringside observers believed Parker, thirty-one, merited the victory but the contender experienced the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Uneventful Match
Buatsi's progress has plateaued in recent years through management issues and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter ready to overcommit in a cagey initial rounds.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to edge the more effective stanzas.
The audience's tolerance diminished during regular grabbing, with the challenger going down multiple occasions during clinches.
Parker closed well, but many rounds were difficult to score. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels Local Rivalry Fight
In the supporting bout, Arthur defeated Rea by split-decision in a terrific local rivalry fight to secure the European light-heavyweight title.
The venue became quiet for a profoundly moving tribute prior to the bout as 10 bells tolled in remembrance of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised match card in the city since the passing of Hatton. As the last bell disappeared, the quiet became a shout of "there's just one Hatton".
The action inside the ropes matched the feeling. Arthur was floored by a left hook directly to the chin in the initial stage, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged soon, heavy swelling developing under his eye as the duo traded punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
Arthur narrowly won the verdict with judges scorecards of draw, 115-113 and 115-112, but both fighters were relentless and courageous, all the qualities their idol the legend represented.
