UK light heavyweight Buatsi made a winning yet disappointing beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight 10-round bout at the boxing arena.
But Parker found success, connecting with powerful individual punches in a fight where the approaches never quite clicked, with excessive holding spoiling the action.
The officials had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They prevail," the victor stated in the ringside as he was faced negative reactions from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, 31, merited the win but the contender endured the second setback of his 28-fight career.
The Champion Secures Win in Slow Match
The fighter's advancement has plateaued in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter willing to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a protective stance to barely take the cleaner stanzas.
The audience's tolerance wore thin during regular grabbing, with Parker going down various instances during clinches.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Motivates All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester battle to capture the European light heavyweight title.
The venue fell silent for a profoundly moving memorial before the fight as ten bells tolled in memory of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's passing. As the final chime faded, the quiet became a chant of "there's just one Ricky Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was floored by a significant blow squarely on the face in the second round, standing uncertainly to his footing on the referee's count.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged soon, significant bruising forming under his face as the fighters exchanged punishing blows.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over 12 rounds.
The victor barely secured the result with official scores of even score, narrow lead and 115-112, but both fighters were relentless and courageous, exactly what their idol the legend embodied.
