British light-heavyweight Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive ten-round contest at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a match where the styles never quite clicked, with excessive holding marring the contest.
The scoring judges judged it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best performance but what defines champions? They prevail," the victor commented in the arena as he was met by negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought the challenger, 31, deserved the decision but the contender experienced the second setback of his 28-match career.
The Champion Earns Win in Dull Match
The fighter's advancement has slowed in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to realize his potential - maybe in what seems like a final roll of the dice - under fresh management.
He started carefully, with neither fighter willing to overcommit in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who utilized a solid defense to barely take the better rounds.
The spectators' acceptance wore thin amid regular grabbing, with Parker going down multiple occasions during clinches.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Arthur beat Bradley Rea by divided decision in a outstanding local rivalry battle to capture the European light-heavyweight championship.
The stadium grew hushed for a extremely emotional memorial ahead of the contest as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime disappeared, the stillness became a chant of "only one Ricky Hatton".
The competition within the ring equaled the sentiment. Arthur was floored by a powerful punch flush on the chin in the early round, getting up unsteadily to his feet on the count of eight.
But the traditional red shorts of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was damaged soon, noticeable damage forming under his face as the pair exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with powerful upward punches as the action seldom decreased over twelve rounds.
Arthur narrowly won the decision with scoring tallies of 114-114, 115-113 and clearer margin, but both fighters were determined and brave, everything their inspiration Hatton stood for.
