UK light heavyweight Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a match where the styles never quite clicked, with frequent clinching spoiling the contest.
Two judges had it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi said in the ringside as he was met by disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the win but the contender experienced the second loss of his 28-match professional journey.
The Champion Secures Victory in Slow Affair
His career development has plateaued in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the future of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with both competitors prepared to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second bout at light-heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who operated with a protective stance to narrowly win the better rounds.
The audience's tolerance wore thin amid frequent holding, with the challenger falling to the floor several times during close exchanges.
The underdog ended stronger, but multiple periods were challenging to assess. Although, ex-champion Carl Frampton - commentating on Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Contest
In the secondary fight, Arthur beat Rea by split-decision in a terrific all-Manchester battle to capture the European light-heavyweight belt.
The stadium became quiet for a deeply poignant memorial before the fight as ten bells rang in remembrance of local hero Hatton, who succumbed 46 years old in September.
It was the first major televised boxing event in the city since Hatton's passing. As the final chime disappeared, the silence became a shout of "there's only one Ricky Hatton".
The action within the ring equaled the feeling. Arthur was floored by a significant blow flush on the face in the early round, standing uncertainly to his footing on the eight count.
But the red-colored equipment of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was injured soon, significant bruising developing under his eye as the fighters traded powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the pace hardly diminished over the full distance.
The victor edged the verdict with judges scorecards of even score, 115-113 and clearer margin, but the two athletes were persistent and full of heart, all the qualities their hero the legend stood for.
