British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a competitive ten-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful single shots in a match where the approaches didn't complement each other, with constant grabbing marring the contest.
The scoring judges had it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my best showing but how do champions respond? They win," the victor commented in the arena as he was greeted with negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers thought Parker, thirty-one, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-match career.
The Champion Claims Win in Uneventful Affair
The fighter's advancement has stalled in recent times through management issues and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to achieve expectations - possibly in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with both competitors ready to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who worked behind a solid defense to barely take the cleaner periods.
The audience's tolerance wore thin during constant clinching, with the challenger slipping to the canvas various instances during clinches.
Parker finished the stronger, but many rounds were difficult to score. However, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still appears challenging.
Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur defeated Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to capture the European light heavyweight championship.
The arena became quiet for a deeply poignant homage before the fight as 10 bells sounded in memory of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime disappeared, the silence became a roar of "there's only one Hatton".
The competition inside the ropes equaled the sentiment. The eventual winner was floored by a left hook directly to the face in the early round, rising shakily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured early, noticeable damage developing under his eye as the pair traded punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the result with judges scorecards of draw, narrow lead and 115-112, but each competitor were persistent and courageous, everything their inspiration the legend embodied.
