UK light heavyweight Buatsi made a winning yet unimpressive beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive ten-round fight at the boxing arena.
But Parker found success, landing some telling clean blows in a match where the techniques failed to mesh, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi stated in the ring as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts felt the challenger, 31, should have been awarded the win but the Derbyshire fighter experienced the second loss of his 28-match professional journey.
The Champion Claims Victory in Uneventful Affair
The fighter's advancement has stalled in recent times through promotional disputes and considerable time of inactivity.
Once tipped as the next star of UK boxing, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors prepared to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second fight at the higher weight class.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who operated with a solid defense to edge the more effective rounds.
The audience's tolerance decreased amid constant clinching, with the challenger falling to the floor various instances during clinches.
The underdog closed well, but many rounds were hard to judge. Although, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Hatton Homage Motivates Local Rivalry Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a excellent all-Manchester fight to win the continental championship.
The venue fell silent for a profoundly moving homage ahead of the contest as 10 bells tolled in honor of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's death. As the concluding sound disappeared, the silence transitioned to a roar of "there's just one Ricky Hatton".
The fighting within the ring reflected the sentiment. Arthur was sent to the canvas by a significant blow directly to the face in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up quickly, significant bruising forming under his eye as the pair exchanged punishing blows.
Rea, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace hardly diminished over the full distance.
Arthur barely secured the result with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were persistent and full of heart, exactly what their idol Hatton represented.
