UK light heavyweight Buatsi made a winning yet disappointing start to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, delivering effective single shots in a contest where the styles never quite clicked, with constant grabbing disrupting the contest.
The officials scored it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best showing but what do champions do? They succeed," Buatsi commented in the ringside as he was faced boos from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in February - to claim a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the win but the British boxer experienced the second loss of his 28-bout career.
The Champion Secures Triumph in Dull Match
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to achieve expectations - perhaps in what seems like a last chance - under fresh management.
He started carefully, with neither fighter prepared to be aggressive in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, causing problems for the favorite, who utilized a solid defense to barely take the better rounds.
The crowd's patience wore thin during frequent holding, with the challenger falling to the floor several times during clinches.
The underdog closed well, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by split-decision in a outstanding Manchester vs Manchester battle to win the European light heavyweight title.
The stadium became quiet for a extremely emotional tribute ahead of the contest as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised match card in the urban center since Hatton's passing. As the final chime ended, the quiet became a chant of "there's only one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was floored by a left hook directly to the face in the second round, rising shakily to his footing on the count of eight.
But the traditional red equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was injured early, noticeable damage developing under his orbital area as the pair traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur barely secured the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but both fighters were persistent and full of heart, exactly what their hero the legend embodied.
