British light heavyweight Buatsi secured a victory yet unimpressive start to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive 10-round bout at the boxing arena.
But the challenger had his moments, delivering effective individual punches in a fight where the styles didn't complement each other, with constant grabbing spoiling the fight.
The officials scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but how do champions respond? They win," the victor stated in the arena as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers believed the challenger, 31, should have been awarded the decision but the contender endured the second loss of his 28-match career.
The Champion Secures Triumph in Uneventful Match
His career development has plateaued in recent times through contract problems and long spells of inactivity.
Once tipped as the next star of British boxing, he now stands trying to realize his potential - maybe in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second fight at light heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who operated with a protective stance to narrowly win the cleaner stanzas.
The audience's tolerance diminished during frequent holding, with the challenger falling to the floor several times during clinches.
Parker closed well, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Motivates Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Rea by split-decision in a terrific Manchester vs Manchester fight to win the European light heavyweight championship.
The stadium became quiet for a profoundly moving homage before the fight as a bell ceremony sounded in remembrance of Manchester's own Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime faded, the silence gave way to a shout of "only one Ricky Hatton".
The fighting within the ring reflected the feeling. Arthur was sent to the canvas by a powerful punch squarely on the face in the initial stage, getting up unsteadily to his feet on the eight count.
But the red-colored shorts of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was injured soon, significant bruising developing under his orbital area as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the decision with judges scorecards of 114-114, close margin and wider gap, but both fighters were determined and courageous, all the qualities their hero the legend stood for.
