British light heavyweight Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a competitive ten-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the techniques never quite clicked, with excessive holding disrupting the action.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best display but what do champions do? They succeed," the victor stated in the arena as he was faced boos from the crowd.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Some ringside observers thought the challenger, 31, deserved the victory but the British boxer experienced the second loss of his 28-match career.
Buatsi Claims Win in Dull Affair
The fighter's advancement has plateaued in recent years through promotional disputes and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to achieve expectations - maybe in what seems like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter willing to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second fight at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to narrowly win the better periods.
The audience's tolerance decreased amid constant clinching, with the challenger falling to the floor various instances during grappling.
Parker closed well, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a excellent local rivalry fight to secure the continental title.
The stadium grew hushed for a deeply poignant tribute ahead of the contest as 10 bells sounded in remembrance of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the last bell ended, the stillness transitioned to a shout of "there's just one Ricky Hatton".
The action within the ring equaled the sentiment. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured early, noticeable damage forming under his orbital area as the duo landed powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were relentless and full of heart, everything their inspiration the legend represented.
