UK light heavyweight Buatsi secured a victory yet underwhelming start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive 10-round bout at the boxing arena.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the techniques failed to mesh, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi stated in the ring as he was faced boos from the audience.
The British fighter got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Various analysts believed the challenger, thirty-one, merited the victory but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
Buatsi Claims Win in Slow Affair
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - maybe in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter prepared to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after suffering a hand injury during the bout, was competing in only his second bout at the higher weight class.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who utilized a solid defense to narrowly win the more effective stanzas.
The spectators' acceptance decreased during frequent holding, with the challenger going down several times during clinches.
The underdog finished the stronger, but many rounds were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding Manchester vs Manchester contest to secure the continental title.
The arena became quiet for a profoundly moving homage before the fight as a bell ceremony rang in memory of Manchester's own Hatton, who died 46 years old in recently.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime disappeared, the quiet gave way to a chant of "there's just one Ricky Hatton".
The fighting during the bout matched the sentiment. The eventual winner was sent to the canvas by a left hook directly to the face in the second round, rising shakily to his footing on the eight count.
But the traditional red equipment of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged soon, noticeable damage developing under his orbital area as the fighters traded powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur edged the verdict with judges scorecards of draw, close margin and 115-112, but each competitor were persistent and full of heart, exactly what their hero Hatton stood for.
