UK light heavyweight Buatsi earned a win yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, landing some telling clean blows in a match where the styles didn't complement each other, with excessive holding disrupting the action.
The scoring judges judged it 96-94 in favor to the winner, with the third a even score.
"It wasn't my best showing but what do champions do? They win," the victor said in the ring as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Some ringside observers thought Parker, 31, should have been awarded the victory but the contender endured the second defeat of his 28-fight professional journey.
Buatsi Secures Victory in Uneventful Affair
Buatsi's progress has plateaued in the past few years through management issues and long spells of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to realize his potential - maybe in what seems like a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to be aggressive in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second fight at the higher weight class.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who operated with a tight guard to narrowly win the better rounds.
The spectators' acceptance diminished because of regular grabbing, with Parker slipping to the canvas multiple occasions during grappling.
Parker closed well, but multiple periods were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to win the continental championship.
The venue fell silent for a extremely emotional homage prior to the bout as a bell ceremony tolled in honor of the city's native Ricky Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the city since Hatton's death. As the concluding sound ended, the quiet gave way to a roar of "there's only one Ricky Hatton".
The action during the bout equaled the emotion. The eventual winner was knocked down by a powerful punch flush on the face in the early round, getting up unsteadily to his position on the referee's count.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, the opponent - in rival City blue - was injured soon, noticeable damage developing under his face as the fighters landed powerful shots.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the pace rarely dropped over the full distance.
The victor narrowly won the decision with judges scorecards of draw, narrow lead and wider gap, but the two athletes were determined and courageous, everything their idol Hatton stood for.
