British light heavyweight Buatsi earned a win yet underwhelming start to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a tight 10-round fight at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a fight where the approaches never quite clicked, with frequent clinching spoiling the fight.
The scoring judges scored it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my finest showing but how do champions respond? They succeed," the victor stated in the arena as he was greeted with negative reactions from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts believed Parker, 31, deserved the victory but the Derbyshire fighter endured the second loss of his 28-fight career.
The Champion Earns Triumph in Uneventful Encounter
Buatsi's progress has stalled in the past few years through management issues and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to realize his potential - possibly in what appears to be a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors prepared to be aggressive in a cagey 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 in the contest, was competing in only his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who operated with a tight guard to barely take the cleaner stanzas.
The audience's tolerance wore thin amid frequent holding, with the challenger going down several times during clinches.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Arthur overcame Rea by split-decision in a terrific all-Manchester fight to win the European light heavyweight championship.
The arena grew hushed for a profoundly moving homage before the fight as ten bells rang in remembrance of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast match card in the location since Hatton's passing. As the final chime disappeared, the quiet became a roar of "only one Ricky Hatton".
The fighting during the bout matched the sentiment. Arthur was floored by a significant blow flush on the jaw in the second round, rising shakily to his footing on the eight count.
But the traditional red equipment of the fighter soon pressed ahead again. On the opposite side, Rea - in rival City blue - was injured early, heavy swelling developing under his eye as the duo landed hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the action seldom decreased over twelve rounds.
The victor edged the result with judges scorecards of even score, close margin and 115-112, but each competitor were persistent and courageous, all the qualities their idol Hatton stood for.
