UK light-heavyweight Buatsi earned a win yet underwhelming beginning to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a tight 10-round fight at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a contest where the styles failed to mesh, with constant grabbing spoiling the fight.
The officials judged it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what do champions do? They win," Buatsi commented in the ringside as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to claim a 20th pro success.
Some ringside observers felt Parker, thirty-one, should have been awarded the win but the British boxer endured the second setback of his 28-bout professional journey.
Buatsi Earns Victory in Uneventful Match
Buatsi's progress has stalled in recent times through promotional disputes and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a last chance - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a cagey initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was competing in only his second appearance at the higher weight class.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who utilized a protective stance to edge the more effective stanzas.
The audience's tolerance wore thin amid regular grabbing, with the challenger falling to the floor multiple occasions during clinches.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still looks steep.
Hatton Homage Inspires All-Manchester Fight
In the co-main event, Arthur overcame Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight belt.
The arena became quiet for a deeply poignant memorial before the fight as ten bells tolled in memory of Manchester's own Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the city since the passing of Hatton. As the concluding sound faded, the stillness transitioned to a roar of "there's only one Hatton".
The fighting during the bout matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the chin in the early round, standing uncertainly to his position on the eight count.
But the traditional red equipment of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was injured quickly, heavy swelling appearing under his eye as the duo exchanged punishing blows.
Rea, 27, delivered effective strikes but Arthur, 34, responded in kind with powerful upward punches as the intensity hardly diminished over 12 rounds.
Arthur barely secured the verdict with judges scorecards of even score, narrow lead and wider gap, but the two athletes were relentless and full of heart, everything their inspiration Hatton represented.
