British light heavyweight Buatsi made a winning yet underwhelming start to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive ten-round fight at the boxing arena.
But Parker landed significant shots, connecting with powerful clean blows in a match where the styles didn't complement each other, with excessive holding spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi commented in the ringside as he was met by boos from the crowd.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts felt Parker, 31, should have been awarded the win but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The Champion Earns Win in Dull Affair
The fighter's advancement has plateaued in recent times through contract problems and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now stands trying to achieve expectations - maybe in what feels like a final roll of the dice - under recent support.
He started carefully, with both competitors willing to take risks in a tentative early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective periods.
The audience's tolerance decreased during frequent holding, with the challenger slipping to the canvas several times during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - on this evidence - still looks steep.
Hatton Memorial Inspires Manchester Derby Contest
In the co-main event, Arthur overcame Rea by close verdict in a terrific all-Manchester battle to win the European light heavyweight championship.
The arena grew hushed for a deeply poignant memorial before the fight as a bell ceremony tolled in memory of the city's native Hatton, who succumbed aged 46 in September.
It was the first major televised fight night in the city since the passing of Hatton. As the concluding sound faded, the stillness gave way to a shout of "only one Hatton".
The fighting during the bout reflected the feeling. The eventual winner was knocked down by a left hook directly to the face in the early round, getting up unsteadily to his footing on the eight count.
But the traditional red attire of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up soon, heavy swelling appearing under his eye as the duo exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur barely secured the result with official scores of 114-114, narrow lead and wider gap, but both fighters were persistent and courageous, everything their idol Hatton stood for.
