UK light-heavyweight Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective individual punches in a match where the techniques failed to mesh, with frequent clinching spoiling the action.
Two judges judged it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but what defines champions? They prevail," Buatsi commented in the arena as he was greeted with negative reactions from the spectators.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Various analysts believed Parker, thirty-one, merited the decision but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The Champion Claims Win in Slow Encounter
Buatsi's progress has plateaued in the past few years through contract problems and considerable time of inactivity.
Earlier forecast as the future of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He opened tentatively, with the two boxers prepared to take risks in a tentative opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second bout at the higher weight class.
By the middle rounds, Parker had made it competitive, causing problems for Buatsi, who worked behind a protective stance to barely take the cleaner stanzas.
The spectators' acceptance wore thin during regular grabbing, with Parker going down various instances during close exchanges.
Parker finished the stronger, but multiple periods were difficult to score. However, ex-champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Arthur overcame Rea by close verdict in a terrific local rivalry battle to secure the continental championship.
The arena fell silent for a deeply poignant homage before the fight as ten bells rang in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell faded, the stillness gave way to a chant of "only one Ricky Hatton".
The action inside the ropes equaled the emotion. The eventual winner was floored by a left hook directly to the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in opposing blue - was injured early, noticeable damage developing under his face as the duo traded hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the intensity seldom decreased over twelve rounds.
Arthur narrowly won the decision with judges scorecards of 114-114, close margin and wider gap, but each competitor were persistent and brave, everything their hero Hatton embodied.
