UK light-heavyweight Buatsi made a winning yet underwhelming start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a close 10-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful single shots in a match where the styles never quite clicked, with excessive holding disrupting the contest.
The officials judged it 96-94 for to the winner, with the third a even score.
"It wasn't my finest display but what defines champions? They succeed," Buatsi stated in the arena as he was greeted with disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, should have been awarded the victory but the contender endured the second defeat of his 28-match career.
The Champion Claims Triumph in Uneventful Affair
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers prepared to take risks in a tentative opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to narrowly win the more effective rounds.
The audience's tolerance diminished because of frequent holding, with Parker going down multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry contest to secure the continental title.
The venue grew hushed for a profoundly moving memorial before the fight as 10 bells tolled in memory of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness became a roar of "only one Ricky Hatton".
The action during the bout reflected the sentiment. The eventual winner was knocked down by a significant blow squarely on the chin in the second round, rising shakily to his feet on the eight count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was injured soon, significant bruising developing under his eye as the duo landed hard punches.
The challenger, 27, landed power punches but the champion, 34, responded in kind with effective uppercuts as the intensity seldom decreased over 12 rounds.
Arthur barely secured the decision with judges scorecards of even score, close margin and 115-112, but each competitor were determined and courageous, all the qualities their inspiration the legend stood for.
