British light-heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round contest at the Manchester venue.
But the challenger had his moments, landing some telling single shots in a fight where the techniques never quite clicked, with constant grabbing spoiling the fight.
The officials scored it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi said in the arena as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Various analysts believed Parker, thirty-one, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-match career.
Buatsi Earns Triumph in Dull Match
Buatsi's progress has slowed in recent times through contract problems and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter prepared to overcommit in a tentative early stages.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after breaking his hand in the contest, was making just his second bout at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to barely take the more effective periods.
The audience's tolerance diminished because of constant clinching, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog closed well, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - on this evidence - still seems difficult.
Hatton Tribute Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Rea by divided decision in a terrific all-Manchester battle to win the European light heavyweight championship.
The venue fell silent for a extremely emotional memorial prior to the bout as 10 bells sounded in honor of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the urban center since Hatton's death. As the final chime ended, the quiet became a roar of "only one Ricky Hatton".
The competition inside the ropes reflected the sentiment. Arthur was sent to the canvas by a powerful punch directly to the jaw in the second round, getting up unsteadily to his footing on the referee's count.
But the traditional red shorts of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was injured soon, noticeable damage appearing under his eye as the pair traded hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over twelve rounds.
Arthur narrowly won the result with scoring tallies of even score, close margin and clearer margin, but the two athletes were persistent and full of heart, exactly what their inspiration Hatton embodied.
