UK light-heavyweight Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round bout at the boxing arena.
But Parker landed significant shots, delivering effective individual punches in a contest where the styles didn't complement each other, with constant grabbing marring the contest.
Two judges scored it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what do champions do? They win," the victor said in the ringside as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers felt Parker, 31, merited the victory but the Derbyshire fighter experienced the second defeat of his 28-fight career.
Buatsi Claims Win in Uneventful Match
The fighter's advancement has stalled in recent times through management issues and considerable time of inactivity.
Previously predicted as the future of British boxing, he now stands trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with both competitors ready to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who utilized a protective stance to edge the more effective rounds.
The audience's tolerance diminished during regular grabbing, with Parker falling to the floor several times during clinches.
Parker closed well, but multiple periods were hard to judge. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Fuels All-Manchester Fight
In the secondary fight, Arthur beat Bradley Rea by split-decision in a terrific local rivalry battle to win the continental belt.
The stadium became quiet for a deeply poignant homage ahead of the contest as ten bells tolled in remembrance of local hero Hatton, who passed away at age 46 in September.
It was the first major televised match card in the city since Hatton's passing. As the concluding sound ended, the silence gave way to a roar of "there's just one Hatton".
The fighting during the bout equaled the emotion. Arthur was knocked down by a significant blow flush on the face in the initial stage, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was damaged quickly, noticeable damage developing under his eye as the fighters traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace hardly diminished over twelve rounds.
Arthur edged the verdict with scoring tallies of even score, close margin and 115-112, but each competitor were determined and brave, everything their hero the legend embodied.
