British light heavyweight Buatsi secured a victory yet underwhelming debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive ten-round fight at the Manchester venue.
But Parker found success, landing some telling single shots in a match where the styles failed to mesh, with frequent clinching disrupting the action.
Two judges judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi said in the ringside as he was faced negative reactions from the crowd.
The British fighter bounced back after his first professional defeat - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Some ringside observers believed Parker, thirty-one, merited the decision but the British boxer endured the second setback of his 28-bout professional journey.
Buatsi Claims Triumph in Slow Match
His career development has slowed in the past few years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to realize his potential - perhaps in what feels like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter prepared to take risks in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who operated with a tight guard to narrowly win the more effective rounds.
The audience's tolerance decreased amid frequent holding, with Parker slipping to the canvas various instances during grappling.
Parker closed well, but several stanzas were challenging to assess. Although, previous titleholder Carl Frampton - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Tribute Inspires All-Manchester Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight belt.
The venue grew hushed for a extremely emotional homage prior to the bout as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who succumbed aged 46 in September.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the concluding sound faded, the stillness gave way to a roar of "there's just one Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a significant blow flush on the face in the early round, getting up unsteadily to his footing on the count of eight.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was marked up soon, heavy swelling forming under his face as the duo exchanged punishing blows.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the decision with scoring tallies of even score, 115-113 and clearer margin, but the two athletes were persistent and brave, all the qualities their idol Hatton stood for.
