UK light heavyweight Buatsi earned a win yet underwhelming beginning to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the styles failed to mesh, with constant grabbing spoiling the contest.
Two judges judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi said in the ringside as he was greeted with negative reactions from the audience.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Various analysts believed Parker, 31, merited the decision but the contender experienced the second defeat of his 28-bout professional journey.
The Champion Earns Victory in Slow Encounter
The fighter's advancement has slowed in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter willing to be aggressive in a tentative initial rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to narrowly win the more effective periods.
The crowd's patience decreased amid regular grabbing, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but multiple periods were hard to judge. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
The victor moves on, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Battle
In the supporting bout, Lyndon Arthur defeated Rea by divided decision in a outstanding Manchester vs Manchester fight to win the European light heavyweight championship.
The venue fell silent for a deeply poignant tribute ahead of the contest as a bell ceremony sounded in memory of the city's native Ricky Hatton, who succumbed 46 years old in last month.
It was the premier televised fight night in the location since Hatton's death. As the final chime ended, the quiet gave way to a shout of "there's only one Ricky Hatton".
The competition within the ring equaled the sentiment. Arthur was knocked down by a left hook directly to the chin in the second round, standing uncertainly to his position on the eight count.
But the red-colored equipment of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was damaged soon, heavy swelling forming under his orbital area as the pair exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over the full distance.
Arthur edged the result with judges scorecards of 114-114, 115-113 and 115-112, but the two athletes were persistent and brave, exactly what their hero Hatton represented.
