British light-heavyweight Buatsi secured a victory yet disappointing debut to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a tight 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling clean blows in a match where the techniques didn't complement each other, with excessive holding disrupting the contest.
The scoring judges judged it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but how do champions respond? They succeed," Buatsi stated in the arena as he was met by disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, thirty-one, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-match career.
Buatsi Earns Win in Uneventful Encounter
His career development has stalled in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to achieve expectations - possibly in what feels like a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter willing to take risks in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second bout at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The crowd's patience wore thin because of constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
The underdog closed well, but many rounds were difficult to score. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Hatton Memorial Fuels Manchester Derby Contest
In the co-main event, Arthur beat Bradley Rea by close verdict in a terrific all-Manchester contest to win the European light heavyweight championship.
The venue grew hushed for a profoundly moving homage ahead of the contest as a bell ceremony sounded in honor of the city's native Hatton, who passed away aged 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime faded, the silence gave way to a shout of "only one Ricky Hatton".
The action during the bout reflected the feeling. Arthur was knocked down by a significant blow squarely on the face in the early round, rising shakily to his footing on the eight count.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up soon, heavy swelling forming under his eye as the duo landed hard punches.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with stinging uppercuts as the intensity rarely dropped over 12 rounds.
Arthur narrowly won the result with official scores of even score, narrow lead and wider gap, but each competitor were determined and full of heart, everything their idol Hatton stood for.
