UK light heavyweight Buatsi earned a win yet underwhelming debut to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful clean blows in a fight where the styles never quite clicked, with frequent clinching spoiling the contest.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what do champions do? They prevail," the victor commented in the arena as he was greeted with disapproval from the audience.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts thought the challenger, 31, merited the win but the contender endured the second setback of his 28-match professional journey.
Buatsi Earns Triumph in Uneventful Affair
His career development has stalled in recent years through contract problems and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - maybe in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter ready to take risks in a tentative opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second appearance at light-heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who operated with a solid defense to narrowly win the more effective periods.
The crowd's patience decreased amid frequent holding, with Parker slipping to the canvas multiple occasions during clinches.
The underdog closed well, but several stanzas were hard to judge. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Hatton Tribute Motivates All-Manchester Contest
In the co-main event, Arthur beat Bradley Rea by close verdict in a terrific all-Manchester fight to win the European light-heavyweight title.
The stadium grew hushed for a profoundly moving tribute before the fight as a bell ceremony rang in memory of the city's native Hatton, who passed away aged 46 in September.
It was the first major televised boxing event in the location since Hatton's death. As the concluding sound ended, the stillness gave way to a roar of "only one Hatton".
The fighting inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a left hook directly to the chin in the early round, standing uncertainly to his position on the count of eight.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was injured quickly, significant bruising developing under his face as the fighters exchanged punishing blows.
Rea, 27, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the intensity rarely dropped over the full distance.
Arthur edged the result with official scores of even score, 115-113 and clearer margin, but the two athletes were persistent and full of heart, all the qualities their idol Hatton embodied.
