UK light heavyweight Buatsi made a winning yet disappointing start to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a split decision in a competitive 10-round bout at the boxing arena.
But Parker had his moments, landing some telling clean blows in a match where the styles failed to mesh, with constant grabbing spoiling the contest.
The officials scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my best performance but what do champions do? They succeed," Buatsi said in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Some ringside observers felt the challenger, 31, merited the victory but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The Champion Claims Triumph in Dull Encounter
The fighter's advancement has stalled in recent times through contract problems and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now finds himself 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 the two boxers willing to take risks in a tentative early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who utilized a tight guard to edge the cleaner periods.
The spectators' acceptance diminished because of regular grabbing, with the challenger going down various instances during close exchanges.
The underdog closed well, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Fuels All-Manchester Contest
In the supporting bout, Arthur overcame Rea by divided decision in a outstanding all-Manchester fight to secure the continental title.
The stadium fell silent for a profoundly moving memorial ahead of the contest as 10 bells rang in memory of local hero Ricky Hatton, who died aged 46 in last month.
It was the initial significant broadcast match card in the urban center since the passing of Hatton. As the final chime disappeared, the silence transitioned to a roar of "there's just one Hatton".
The competition within the ring equaled the feeling. Arthur was knocked down by a left hook squarely on the chin in the initial stage, rising shakily to his footing on the eight count.
But the Manchester United-red attire of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was injured quickly, significant bruising developing under his face as the duo traded powerful shots.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action seldom decreased over twelve rounds.
The victor narrowly won the verdict with scoring tallies of even score, 115-113 and wider gap, but the two athletes were determined and full of heart, all the qualities their hero the legend represented.
