UK light-heavyweight Buatsi secured a victory yet unimpressive debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a close 10-round bout at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a fight where the approaches never quite clicked, with excessive holding marring the action.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but how do champions respond? They win," the victor stated in the ringside as he was greeted with boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts thought the challenger, 31, merited the victory but the contender endured the second loss of his 28-match career.
The Champion Earns Win in Slow Affair
The fighter's advancement has stalled in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to realize his potential - perhaps in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter prepared to take risks in a cagey opening few 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 participating in his second bout at the higher weight class.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a solid defense to edge the more effective periods.
The spectators' acceptance diminished because of frequent holding, with the challenger going down multiple occasions during clinches.
The underdog finished the stronger, but several stanzas were hard to judge. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a excellent local rivalry battle to win the European light-heavyweight title.
The venue fell silent for a deeply poignant memorial prior to the bout as a bell ceremony rang in honor of local hero Ricky Hatton, who passed away aged 46 in September.
It was the first major televised match card in the city since Hatton's death. As the last bell disappeared, the silence gave way to a shout of "there's just one Ricky Hatton".
The competition within the ring matched the sentiment. Arthur was floored by a powerful punch squarely on the face in the early round, rising shakily to his feet on the referee's count.
But the red-colored shorts of the fighter soon advanced again. From the other corner, Rea - in opposing blue - was injured early, noticeable damage forming under his orbital area as the duo traded punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with powerful upward punches as the action hardly diminished over twelve rounds.
The victor narrowly won the verdict with scoring tallies of even score, narrow lead and 115-112, but both fighters were persistent and brave, everything their idol Hatton stood for.
