British light-heavyweight Buatsi earned a win yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling clean blows in a match where the styles didn't complement each other, with constant grabbing disrupting the contest.
The officials had it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest performance but how do champions respond? They succeed," the victor commented in the ring as he was faced negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an epic battle with his previous opponent in February - to claim a twentieth professional win.
Some ringside observers believed the challenger, 31, merited the victory but the British boxer suffered the second defeat of his 28-bout career.
The Champion Secures Victory in Uneventful Encounter
Buatsi's progress has plateaued in recent times through promotional disputes and extended periods of lack of fights.
Previously predicted as the next star of UK boxing, he now finds himself trying to achieve expectations - maybe in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter willing to overcommit in a tentative initial rounds.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for the favorite, who worked behind a tight guard to barely take the cleaner stanzas.
The crowd's patience wore thin during regular grabbing, with the challenger falling to the floor various instances during clinches.
The underdog ended stronger, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Homage Fuels Manchester Derby Contest
In the co-main event, Arthur defeated Rea by close verdict in a excellent local rivalry battle to capture the European light heavyweight championship.
The stadium became quiet for a deeply poignant tribute before the fight as a bell ceremony tolled in honor of the city's native Hatton, who passed away at age 46 in September.
It was the first major televised boxing event in the city since Hatton's death. As the concluding sound disappeared, the quiet gave way to a roar of "only one Ricky Hatton".
The fighting within the ring equaled the sentiment. Arthur was sent to the canvas by a powerful punch flush on the chin in the early round, rising shakily to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in opposing blue - was damaged early, noticeable damage developing under his face as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur edged the verdict with official scores of even score, narrow lead and clearer margin, but the two athletes were relentless and full of heart, everything their idol the legend embodied.
