UK light heavyweight Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a split decision in a competitive 10-round bout at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a fight where the techniques failed to mesh, with frequent clinching marring the action.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They prevail," the victor stated in the arena as he was greeted with disapproval from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to claim a 20th pro success.
Various analysts felt the challenger, 31, deserved the decision but the British boxer suffered the second setback of his 28-fight professional journey.
The Champion Secures Win in Slow Affair
Buatsi's progress has slowed in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with both competitors willing to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second bout at light-heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for Buatsi, who utilized a tight guard to narrowly win the better stanzas.
The audience's tolerance diminished because of frequent holding, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but many rounds were difficult to score. Nevertheless, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Memorial Inspires Local Rivalry Contest
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester battle to capture the European light-heavyweight title.
The stadium grew hushed for a deeply poignant homage ahead of the contest as ten bells sounded in honor of local hero Ricky Hatton, who died 46 years old in September.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound faded, the silence gave way to a chant of "there's just one Hatton".
The fighting within the ring matched the sentiment. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the second round, getting up unsteadily to his footing on the eight count.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, the opponent - in rival City blue - was damaged soon, significant bruising forming under his eye as the pair landed powerful shots.
The challenger, 27, landed power punches but Arthur, 34, matched the intensity with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur narrowly won the decision with official scores of 114-114, narrow lead and 115-112, but both fighters were persistent and full of heart, everything their idol the legend embodied.
