British light heavyweight Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a points victory over Zach Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a majority decision in a tight 10-round fight at the Manchester venue.
But Parker landed significant shots, landing some telling individual punches in a contest where the approaches didn't complement each other, with constant grabbing marring the action.
Two judges scored 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 succeed," the victor said in the arena as he was faced disapproval from the audience.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th pro success.
Some ringside observers believed Parker, thirty-one, merited the win but the Derbyshire fighter experienced the second loss of his 28-match career.
The Champion Secures Victory in Dull Encounter
The fighter's advancement has plateaued in recent years through management issues and extended periods of lack of fights.
Previously predicted as the next star of the British fight scene, he now stands trying to fulfil that early promise - maybe in what feels like a last chance - under fresh management.
He began cautiously, with both competitors ready to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who operated with a tight guard to edge the better stanzas.
The audience's tolerance diminished because of regular grabbing, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. However, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Fuels Local Rivalry Fight
In the secondary fight, Arthur beat Rea by close verdict in a excellent Manchester vs Manchester fight to capture the European light heavyweight championship.
The stadium became quiet for a extremely emotional memorial before the fight as 10 bells rang in honor of Manchester's own Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's death. As the concluding sound faded, the stillness gave way to a shout of "only one Hatton".
The action inside the ropes matched the sentiment. Arthur was floored by a left hook squarely on the face in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red attire of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was damaged soon, noticeable damage forming under his orbital area as the duo traded hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over twelve rounds.
The victor edged the decision with official scores of even score, close margin and clearer margin, but each competitor were determined and brave, exactly what their hero the legend represented.
