British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a tight 10-round fight at the boxing arena.
But the challenger had his moments, connecting with powerful individual punches in a match where the techniques never quite clicked, with frequent clinching spoiling the contest.
The scoring judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my finest showing but how do champions respond? They prevail," Buatsi commented in the ring as he was faced negative reactions from the crowd.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts felt Parker, thirty-one, deserved the victory but the British boxer suffered the second defeat of his 28-match career.
The Champion Claims Triumph in Dull Encounter
His career development has stalled in recent years through promotional disputes and extended periods of lack of fights.
Previously predicted as the next star of British boxing, he now stands trying to achieve expectations - possibly in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who operated with a tight guard to edge the more effective rounds.
The crowd's patience wore thin because of constant clinching, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a excellent Manchester vs Manchester fight to secure the European light heavyweight championship.
The venue grew hushed for a deeply poignant homage prior to the bout as 10 bells rang in honor of the city's native Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the location since Hatton's death. As the last bell ended, the silence gave way to a roar of "there's just one Hatton".
The fighting during the bout matched the feeling. The eventual winner was floored by a powerful punch flush on the chin in the second round, rising shakily to his position on the referee's count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was injured early, heavy swelling forming under his orbital area as the duo traded powerful shots.
The challenger, 27, landed power punches but Arthur, thirty-four, responded in kind with powerful upward punches as the intensity rarely dropped over the full distance.
The victor edged the decision with official scores of draw, 115-113 and clearer margin, but each competitor were determined and brave, all the qualities their idol Hatton stood for.
