British light heavyweight Buatsi secured a victory yet unimpressive start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a close ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the styles never quite clicked, with frequent clinching marring the contest.
Two judges had it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They succeed," Buatsi stated in the ringside as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to claim a 20th career victory.
Several boxing experts believed Parker, thirty-one, deserved the win but the contender experienced the second setback of his 28-bout career.
The Champion Earns Win in Dull Encounter
The fighter's advancement has slowed in recent years through contract problems and considerable time of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to barely take the better stanzas.
The spectators' acceptance decreased during frequent holding, with the challenger going down various instances during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Memorial Inspires All-Manchester Battle
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a excellent local rivalry battle to win the European light heavyweight championship.
The venue fell silent for a deeply poignant tribute before the fight as ten bells sounded in memory of local hero Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a roar of "there's just one Ricky Hatton".
The competition within the ring equaled the feeling. Arthur was knocked down by a powerful punch flush on the face in the initial stage, getting up unsteadily to his feet on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was marked up quickly, significant bruising developing under his eye as the fighters traded powerful shots.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur barely secured the result with official scores of even score, close margin and clearer margin, but both fighters were persistent and full of heart, exactly what their hero Hatton stood for.
