British light heavyweight Buatsi secured a victory yet unimpressive debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a close ten-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the approaches failed to mesh, with excessive holding disrupting the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," Buatsi commented in the arena as he was greeted with boos from the audience.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Various analysts thought Parker, 31, deserved the victory but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Secures Win in Dull Encounter
His career development has plateaued in recent times through management issues and considerable time of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to achieve expectations - possibly in what feels like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers prepared to take risks in a cagey early stages.
Parker, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to edge the better periods.
The spectators' acceptance decreased amid constant clinching, with the challenger going down multiple occasions during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Hatton Homage Motivates All-Manchester Fight
In the co-main event, Arthur overcame Bradley Rea by close verdict in a excellent local rivalry contest to secure the continental belt.
The stadium grew hushed for a deeply poignant memorial before the fight as 10 bells tolled in remembrance of the city's native Hatton, who passed away aged 46 in recently.
It was the premier televised boxing event in the urban center since the passing of Hatton. As the concluding sound disappeared, the silence gave way to a chant of "there's only one Ricky Hatton".
The fighting inside the ropes reflected the emotion. Arthur was knocked down by a powerful punch directly to the chin in the initial stage, rising shakily to his feet on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged soon, heavy swelling developing under his face as the pair landed powerful shots.
Rea, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
Arthur edged the result with official scores of 114-114, 115-113 and clearer margin, but both fighters were relentless and full of heart, everything their inspiration the legend represented.
