British light heavyweight Buatsi earned a win yet unimpressive beginning to his career under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive 10-round contest at the boxing arena.
But Parker found success, delivering effective single shots in a match where the techniques failed to mesh, with frequent clinching marring the action.
The scoring judges judged it 96-94 for to Buatsi, with the third a even score.
"It wasn't my greatest display but how do champions respond? They prevail," the victor commented in the ringside as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in February - to secure a 20th career victory.
Several boxing experts thought Parker, thirty-one, deserved the win but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
The Champion Secures Win in Uneventful Match
Buatsi's progress has slowed in recent years through contract problems and long spells of lack of fights.
Once tipped as the future of the British fight scene, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He started carefully, with both competitors ready to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at super-middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who operated with a protective stance to narrowly win the cleaner rounds.
The spectators' acceptance wore thin during regular grabbing, with Parker falling to the floor various instances during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Russian star Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Homage Motivates Manchester Derby Fight
In the secondary fight, Arthur beat Rea by close verdict in a outstanding all-Manchester fight to win the European light heavyweight title.
The arena became quiet for a deeply poignant memorial prior to the bout as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the concluding sound faded, the quiet gave way to a roar of "only one Hatton".
The competition inside the ropes reflected the feeling. The eventual winner was knocked down by a left hook directly to the face in the initial stage, standing uncertainly to his footing on the eight count.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was marked up soon, heavy swelling appearing under his face as the fighters traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over the full distance.
The victor narrowly won the result with scoring tallies of 114-114, narrow lead and 115-112, but both fighters were persistent and courageous, exactly what their hero Hatton stood for.
