British light heavyweight Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger had his moments, delivering effective single shots in a fight where the approaches failed to mesh, with frequent clinching spoiling the fight.
Two judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest showing but what defines champions? They succeed," Buatsi commented in the arena as he was greeted with boos from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Some ringside observers believed the challenger, 31, should have been awarded the win but the British boxer experienced the second loss of his 28-bout career.
Buatsi Earns Victory in Slow Match
Buatsi's progress has slowed in the past few years through promotional disputes and extended periods of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with the two boxers willing to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to barely take the more effective periods.
The crowd's patience wore thin because of regular grabbing, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but many rounds were difficult to score. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, giving Buatsi just only one stanza.
The victor advances, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Fight
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to secure the continental title.
The stadium grew hushed for a deeply poignant tribute prior to the bout as 10 bells tolled in memory of local hero Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime faded, the quiet transitioned to a roar of "there's only one Hatton".
The competition during the bout reflected the feeling. Arthur was sent to the canvas by a powerful punch squarely on the face in the second round, rising shakily to his footing on the referee's count.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was injured early, significant bruising forming under his face as the fighters landed hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace hardly diminished over 12 rounds.
Arthur barely secured the decision with official scores of even score, 115-113 and wider gap, but the two athletes were persistent and courageous, exactly what their idol the legend represented.
