British light heavyweight Buatsi earned a win yet underwhelming start to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a tight 10-round fight at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a fight where the styles failed to mesh, with constant grabbing marring the contest.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi commented in the ring as he was faced negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to earn a twentieth professional win.
Various analysts believed the challenger, thirty-one, merited the decision but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
Buatsi Claims Triumph in Uneventful Encounter
Buatsi's progress has slowed in recent times through promotional disputes and considerable time of lack of fights.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - possibly in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors willing to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second fight at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who utilized a solid defense to edge the better stanzas.
The spectators' acceptance wore thin amid frequent holding, with the challenger falling to the floor various instances during clinches.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the likes of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Motivates All-Manchester Battle
In the supporting bout, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester contest to win the European light heavyweight title.
The stadium became quiet for a extremely emotional memorial prior to the bout as a bell ceremony sounded in memory of local hero Hatton, who died at age 46 in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the final chime faded, the silence became a chant of "only one Ricky Hatton".
The competition during the bout equaled the emotion. Arthur was floored by a left hook flush on the jaw in the second round, standing uncertainly to his position on the count of eight.
But the traditional red attire of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was injured early, heavy swelling appearing under his eye as the pair landed hard punches.
The challenger, 27, landed power punches but the champion, thirty-four, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
The victor edged the result with judges scorecards of even score, narrow lead and 115-112, but both fighters were determined and courageous, exactly what their inspiration Hatton stood for.
