British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the approaches failed to mesh, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 in favor to the winner, with the remaining official a 95-95.
"It wasn't my greatest display but what do champions do? They succeed," the victor stated in the arena as he was met by boos from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers believed the challenger, 31, deserved the win but the contender suffered the second setback of his 28-match career.
The Champion Earns Victory in Slow Affair
The fighter's advancement has stalled in recent times through promotional disputes and extended periods of lack of fights.
Earlier forecast as the future of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to take risks in a calculated opening few rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who utilized a solid defense to edge the better rounds.
The crowd's patience diminished during frequent holding, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Rea by split-decision in a terrific Manchester vs Manchester battle to capture the European light heavyweight championship.
The venue grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony rang in honor of local hero Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the last bell disappeared, the silence became a chant of "there's only one Hatton".
The competition within the ring equaled the sentiment. Arthur was floored by a left hook directly to the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in rival City blue - was damaged early, noticeable damage appearing under his eye as the fighters landed hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the verdict with scoring tallies of draw, narrow lead and 115-112, but both fighters were relentless and brave, exactly what their inspiration Hatton embodied.
