UK light-heavyweight Buatsi earned a win yet disappointing beginning to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a close 10-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a contest where the techniques didn't complement each other, with frequent clinching marring the contest.
Two judges scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best performance but what do champions do? They prevail," the victor said in the ring as he was faced boos from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with Callum Smith in February - to claim a 20th career victory.
Some ringside observers thought Parker, 31, merited the victory but the Derbyshire fighter experienced the second loss of his 28-bout career.
Buatsi Secures Triumph in Dull Encounter
Buatsi's progress has stalled in the past few years through management issues and long spells of lack of fights.
Previously predicted as the next star of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a ultimate opportunity - under new promotional backing.
He opened tentatively, with neither fighter prepared to overcommit in a tentative opening few rounds.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who worked behind a solid defense to narrowly win the more effective stanzas.
The spectators' acceptance wore thin because of frequent holding, with the challenger going down several times during grappling.
Parker ended stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a excellent Manchester vs Manchester contest to win the European light heavyweight belt.
The stadium became quiet for a deeply poignant tribute before the fight as a bell ceremony rang in remembrance of local hero Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast match card in the city since Hatton's passing. As the concluding sound faded, the silence transitioned to a roar of "only one Ricky Hatton".
The competition during the bout equaled the sentiment. The eventual winner was sent to the canvas by a significant blow directly to the jaw in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red equipment of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up early, noticeable damage developing under his face as the pair exchanged punishing blows.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
The victor edged the decision with official scores of even score, narrow lead and clearer margin, but the two athletes were persistent and courageous, everything their idol the legend embodied.
