British light heavyweight Buatsi made a winning yet unimpressive debut to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight 10-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a contest where the styles never quite clicked, with excessive holding disrupting the contest.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi commented in the arena as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts believed the challenger, 31, deserved the victory but the Derbyshire fighter suffered the second defeat of his 28-bout career.
The Champion Secures Victory in Uneventful Match
Buatsi's progress has slowed in the past few years through management issues and considerable time of lack of fights.
Earlier forecast as the next star of the British fight scene, he now is positioned trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter willing to be aggressive in a cagey initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who operated with a tight guard to barely take the cleaner rounds.
The spectators' acceptance decreased amid constant clinching, with the challenger falling to the floor various instances during grappling.
Parker finished the stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Ricky Hatton Homage Motivates All-Manchester Battle
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a terrific local rivalry fight to secure the European light-heavyweight title.
The stadium grew hushed for a profoundly moving tribute before the fight as a bell ceremony rang in honor of the city's native Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since Hatton's death. As the final chime disappeared, the silence gave way to a chant of "there's only one Ricky Hatton".
The competition inside the ropes reflected the emotion. Arthur was floored by a left hook flush on the jaw in the early round, rising shakily to his position on the referee's count.
But the traditional red attire of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was marked up quickly, heavy swelling appearing under his face as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over twelve rounds.
The victor narrowly won the result with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were persistent and courageous, all the qualities their inspiration Hatton represented.
