UK light-heavyweight Buatsi earned a win yet disappointing start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a tight ten-round contest at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a fight where the styles failed to mesh, with excessive holding marring the contest.
The officials scored it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi said in the ringside as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Various analysts thought Parker, thirty-one, should have been awarded the win but the contender suffered the second setback of his 28-match career.
The Champion Claims Win in Uneventful Match
His career development has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He opened tentatively, with the two boxers willing to be aggressive in a cagey initial rounds.
The challenger, 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 fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to narrowly win the better rounds.
The audience's tolerance decreased because of constant clinching, with the challenger falling to the floor several times during grappling.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur beat Rea by close verdict in a excellent all-Manchester fight to capture the European light heavyweight title.
The venue became quiet for a profoundly moving homage prior to the bout as ten bells sounded in memory of the city's native Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the concluding sound disappeared, the stillness became a shout of "there's just one Hatton".
The competition during the bout reflected the sentiment. Arthur was knocked down by a significant blow squarely on the face in the initial stage, standing uncertainly to his feet on the count of eight.
But the traditional red attire of the fighter soon advanced again. From the other corner, the opponent - in competitive blue - was marked up early, noticeable damage appearing under his eye as the fighters landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the result with official scores of draw, narrow lead and clearer margin, but each competitor were persistent and courageous, everything their inspiration Hatton represented.
