British light-heavyweight Buatsi made a winning yet unimpressive beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight ten-round fight at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a fight where the approaches didn't complement each other, with constant grabbing disrupting the contest.
The scoring judges scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best showing but how do champions respond? They succeed," Buatsi commented in the ringside as he was faced negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed the challenger, 31, should have been awarded the win but the contender experienced the second loss of his 28-bout professional journey.
Buatsi Secures Triumph in Slow Match
Buatsi's progress has slowed in recent times through contract problems and long spells of lack of fights.
Once tipped as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what seems like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for the favorite, who operated with a protective stance to barely take the better periods.
The crowd's patience wore thin during regular grabbing, with Parker falling to the floor various instances during close exchanges.
Parker finished the stronger, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Fuels Local Rivalry Fight
In the supporting bout, Arthur overcame Rea by split-decision in a terrific local rivalry contest to capture the European light-heavyweight belt.
The venue became quiet for a extremely emotional homage prior to the bout as a bell ceremony rang in remembrance of Manchester's own Hatton, who passed away 46 years old in last month.
It was the first major televised fight night in the location since the passing of Hatton. As the last bell ended, the quiet became a shout of "there's just one Hatton".
The action during the bout reflected the emotion. Arthur was knocked down by a powerful punch directly to the face in the initial stage, rising shakily to his footing on the referee's count.
But the traditional red equipment of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was damaged quickly, significant bruising forming under his face as the fighters exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor edged the decision with judges scorecards of draw, narrow lead and 115-112, but each competitor were relentless and brave, everything their hero the legend embodied.
