British light-heavyweight Buatsi secured a victory yet disappointing beginning to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a contest where the techniques failed to mesh, with constant grabbing disrupting the fight.
Two judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my finest performance but what defines champions? They prevail," the victor stated in the arena as he was faced boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, deserved the win but the contender experienced the second loss of his 28-bout professional journey.
Buatsi Secures Win in Dull Match
His career development has slowed in recent years through management issues and long spells of lack of fights.
Once tipped as the next star of UK boxing, he now is positioned trying to achieve expectations - maybe in what feels like a final roll of the dice - under recent support.
He began cautiously, with the two boxers prepared to take risks in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to barely take the better periods.
The audience's tolerance diminished because of frequent holding, with the challenger going down multiple occasions during grappling.
The underdog closed well, but several stanzas were difficult to score. However, ex-champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just one round.
The victor advances, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the journey to titles - on this evidence - still looks steep.
Hatton Homage Fuels All-Manchester Battle
In the co-main event, Lyndon Arthur beat Rea by close verdict in a excellent all-Manchester fight to win the European light-heavyweight belt.
The venue became quiet for a extremely emotional homage prior to the bout as ten bells sounded in remembrance of the city's native Ricky 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 final chime disappeared, the silence transitioned to a roar of "there's only one Hatton".
The fighting within the ring reflected the feeling. The eventual winner was knocked down by a left hook directly to the face in the early round, standing uncertainly to his position on the referee's count.
But the Manchester United-red attire of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured early, noticeable damage forming under his face as the pair landed punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur narrowly won the verdict with judges scorecards of even score, 115-113 and 115-112, but each competitor were relentless and full of heart, exactly what their idol Hatton represented.
