British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight ten-round contest at the boxing arena.
But Parker found success, delivering effective single shots in a match where the styles didn't complement each other, with frequent clinching marring the contest.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor commented in the arena as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with Callum Smith in February - to earn a 20th pro success.
Various analysts thought Parker, 31, deserved the win but the British boxer experienced the second setback of his 28-fight professional journey.
The Champion Secures Win in Uneventful Encounter
His career development has plateaued in the past few years through contract problems and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now stands trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He opened tentatively, with the two boxers ready to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who utilized a solid defense to edge the better periods.
The crowd's patience decreased amid constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific Manchester vs Manchester contest to win the European light heavyweight belt.
The venue became quiet for a extremely emotional homage before the fight as a bell ceremony tolled in honor of local hero Hatton, who succumbed 46 years old in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the final chime disappeared, the silence became a roar of "there's only one Ricky Hatton".
The fighting within the ring reflected the feeling. Arthur was sent to the canvas by a powerful punch flush on the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red shorts of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was marked up quickly, noticeable damage developing under his eye as the duo landed powerful shots.
Rea, 27, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over the full distance.
The victor barely secured the decision with judges scorecards of 114-114, close margin and 115-112, but each competitor were determined and courageous, everything their idol Hatton embodied.
