UK light-heavyweight Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a split decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective single shots in a fight where the approaches failed to mesh, with constant grabbing spoiling the fight.
Two judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my finest showing but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with boos from the audience.
The British fighter got back to winning after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Various analysts felt Parker, thirty-one, deserved the decision but the contender suffered the second loss of his 28-match career.
The Champion Secures Triumph in Dull Encounter
His career development has slowed in recent times through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors ready to take risks in a tentative early stages.
The challenger, whose only previous defeat came at super middleweight against John Ryder in 2022 after damaging his hand in the contest, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for Buatsi, who worked behind a tight guard to narrowly win the more effective periods.
The crowd's patience diminished during constant clinching, with the challenger falling to the floor several times during clinches.
The underdog closed well, but many rounds were hard to judge. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Motivates All-Manchester Fight
In the co-main event, Arthur overcame Bradley Rea by close verdict in a excellent local rivalry fight to capture the continental championship.
The venue became quiet for a profoundly moving homage prior to the bout as ten bells tolled in remembrance of local hero Ricky Hatton, who died 46 years old in last month.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the final chime faded, the quiet became a roar of "only one Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was knocked down by a left hook flush on the jaw in the initial stage, getting up unsteadily to his feet on the eight count.
But the traditional red equipment of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was damaged quickly, noticeable damage developing under his orbital area as the fighters exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the pace hardly diminished over the full distance.
Arthur edged the decision with scoring tallies of even score, narrow lead and clearer margin, but the two athletes were persistent and full of heart, everything their inspiration Hatton embodied.
