UK light heavyweight Buatsi made a winning yet disappointing debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive ten-round contest at the boxing arena.
But the challenger landed significant shots, delivering effective individual punches in a match where the approaches failed to mesh, with constant grabbing marring the fight.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest performance but how do champions respond? They prevail," Buatsi stated in the arena as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts believed Parker, 31, should have been awarded the win but the Derbyshire fighter suffered the second loss of his 28-match professional journey.
The Champion Secures Win in Uneventful Encounter
The fighter's advancement has slowed in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with both competitors ready to take risks in a calculated early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for Buatsi, who operated with a tight guard to barely take the better rounds.
The audience's tolerance decreased amid regular grabbing, with Parker falling to the floor multiple occasions during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. Although, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Arthur beat Rea by divided decision in a outstanding Manchester vs Manchester contest to secure the European light-heavyweight belt.
The stadium became quiet for a extremely emotional memorial before the fight as 10 bells rang in remembrance of the city's native Ricky Hatton, who succumbed 46 years old in recently.
It was the first major televised fight night in the location since Hatton's death. As the final chime ended, the stillness transitioned to a chant of "there's only one Ricky Hatton".
The fighting within the ring matched the feeling. Arthur was floored by a powerful punch directly to the jaw in the early round, getting up unsteadily to his footing on the count of eight.
But the traditional red shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured early, significant bruising forming under his orbital area as the pair exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur barely secured the verdict with scoring tallies of 114-114, close margin and wider gap, but each competitor were persistent and courageous, everything their inspiration the legend represented.
