UK light-heavyweight Buatsi earned a win yet disappointing beginning to life under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a split decision in a close 10-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with excessive holding spoiling the contest.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi said in the arena as he was faced boos from the spectators.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Some ringside observers felt Parker, thirty-one, deserved the decision but the contender endured the second loss of his 28-match career.
The Champion Earns Victory in Uneventful Match
His career development has slowed in the past few years through promotional disputes and considerable time of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to realize his potential - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers willing to overcommit in a cagey early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who utilized a tight guard to barely take the cleaner periods.
The crowd's patience wore thin amid regular grabbing, with Parker slipping to the canvas several times during close exchanges.
Parker closed well, but multiple periods were difficult to score. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates Local Rivalry Contest
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific all-Manchester fight to capture the continental belt.
The stadium became quiet for a deeply poignant homage before the fight as a bell ceremony rang in memory of Manchester's own Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised match card in the urban center since Hatton's passing. As the last bell ended, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The action inside the ropes reflected the sentiment. Arthur was floored by a powerful punch flush on the chin in the early round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was damaged early, heavy swelling forming under his orbital area as the duo traded punishing blows.
Rea, 27, delivered effective strikes but Arthur, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over 12 rounds.
Arthur narrowly won the result with scoring tallies of draw, close margin and 115-112, but the two athletes were determined and full of heart, all the qualities their hero Hatton stood for.
