British light-heavyweight Buatsi secured a victory yet unimpressive debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive ten-round contest at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a match where the styles failed to mesh, with constant grabbing spoiling the fight.
The officials judged it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," the victor commented in the arena as he was faced disapproval from the spectators.
The British fighter got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt the challenger, thirty-one, merited the victory but the contender endured the second loss of his 28-fight professional journey.
The Champion Claims Win in Uneventful Affair
Buatsi's progress has stalled in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to realize his potential - maybe in what appears to be a last chance - under new promotional backing.
He began cautiously, with the two boxers willing to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who operated with a solid defense to narrowly win the cleaner periods.
The spectators' acceptance wore thin because of constant clinching, with the challenger going down several times during clinches.
Parker closed well, but several stanzas were difficult to score. Although, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of power puncher David Benavidez, and Russian champion Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Homage Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a terrific local rivalry fight to capture the European light-heavyweight championship.
The arena became quiet for a profoundly moving tribute ahead of the contest as 10 bells rang in remembrance of the city's native Ricky Hatton, who passed away at age 46 in September.
It was the premier televised match card in the urban center since Hatton's death. As the concluding sound ended, the stillness gave way to a chant of "there's just one Hatton".
The action during the bout reflected the sentiment. Arthur was knocked down by a powerful punch directly to the face in the second round, rising shakily to his footing on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, Rea - in rival City blue - was injured soon, noticeable damage developing under his face as the duo exchanged punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur narrowly won the decision with scoring tallies of draw, close margin and wider gap, but each competitor were determined and full of heart, all the qualities their hero Hatton represented.
