British light heavyweight Buatsi earned a win yet disappointing beginning to his career under fresh promotional backing with a unanimous decision over Zach Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a competitive 10-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective clean blows in a match where the approaches failed to mesh, with constant grabbing marring the fight.
The officials had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what defines champions? They succeed," Buatsi commented in the ringside as he was greeted with boos from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to claim a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the win but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
The Champion Claims Triumph in Slow Affair
The fighter's advancement has plateaued in recent years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors ready to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who worked behind a solid defense to narrowly win the more effective stanzas.
The spectators' acceptance decreased because of frequent holding, with the challenger going down several times during clinches.
Parker finished the stronger, but multiple periods were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor moves on, but with the presence of power puncher David Benavidez, and Russian champion Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels Manchester Derby Battle
In the co-main event, Arthur overcame Rea by divided decision in a outstanding all-Manchester battle to secure the European light-heavyweight belt.
The arena became quiet for a profoundly moving memorial before the fight as 10 bells rang in honor of local hero Hatton, who died 46 years old in recently.
It was the initial significant broadcast match card in the city since Hatton's death. As the concluding sound disappeared, the stillness became a chant of "there's only one Ricky Hatton".
The competition during the bout matched the sentiment. The eventual winner was sent to the canvas by a left hook flush on the chin in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was damaged early, heavy swelling developing under his face as the fighters traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur barely secured the decision with judges scorecards of 114-114, close margin and wider gap, but each competitor were persistent and brave, all the qualities their inspiration the legend embodied.
