UK light-heavyweight Buatsi secured a victory yet underwhelming start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a split decision in a tight 10-round bout at the boxing arena.
But Parker found success, landing some telling individual punches in a contest where the approaches didn't complement each other, with excessive holding marring the fight.
Two judges had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They succeed," the victor said in the arena as he was met by disapproval 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 20th career victory.
Some ringside observers felt Parker, 31, should have been awarded the victory but the contender experienced the second setback of his 28-match professional journey.
The Champion Earns Win in Uneventful Match
His career development has stalled in recent times through promotional disputes and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now stands trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors ready to overcommit in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second fight at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the better stanzas.
The spectators' acceptance decreased during constant clinching, with the challenger falling to the floor several times during close exchanges.
Parker closed well, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the caliber of hard hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Hatton Homage Motivates Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a terrific all-Manchester fight to win the continental championship.
The venue became quiet for a extremely emotional tribute ahead of the contest as a bell ceremony sounded in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime faded, the quiet gave way to a chant of "there's just one Hatton".
The action during the bout equaled the feeling. Arthur was floored by a powerful punch squarely on the face in the early round, getting up unsteadily to his feet on the count of eight.
But the traditional red attire of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was injured early, heavy swelling appearing under his face as the fighters landed punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
The victor narrowly won the verdict with official scores of draw, close margin and wider gap, but each competitor were persistent and full of heart, everything their idol Hatton represented.
