British light-heavyweight Buatsi secured a victory yet unimpressive start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a contest where the styles didn't complement each other, with constant grabbing marring the action.
The officials scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest display but what defines champions? They win," the victor commented in the ringside as he was met by disapproval from the audience.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Various analysts felt the challenger, thirty-one, should have been awarded the win but the contender endured the second defeat of his 28-match career.
The Champion Earns Win in Dull Match
The fighter's advancement has slowed in recent times through management issues and extended periods of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand in the contest, was making just his second appearance at light-heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who utilized a tight guard to edge the more effective stanzas.
The spectators' acceptance wore thin amid constant clinching, with the challenger going down various instances during clinches.
The underdog finished the stronger, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the secondary fight, Arthur overcame Rea by close verdict in a outstanding local rivalry fight to capture the continental belt.
The venue fell silent for a profoundly moving homage prior to the bout as 10 bells tolled in memory of the city's native Ricky Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the location since the passing of Hatton. As the concluding sound disappeared, the silence gave way to a roar of "only one Ricky Hatton".
The fighting inside the ropes equaled the sentiment. The eventual winner was knocked down by a significant blow directly to the face in the early round, rising shakily to his footing on the eight count.
But the traditional red shorts of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was damaged early, heavy swelling appearing under his eye as the pair landed powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur barely secured the result with official scores of draw, close margin and clearer margin, but the two athletes were relentless and full of heart, exactly what their idol the legend represented.
