British light heavyweight Buatsi earned a win yet unimpressive start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the styles didn't complement each other, with excessive holding disrupting the fight.
The scoring judges judged it 96-94 for to Buatsi, with the final judge a 95-95.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi said in the ring as he was faced negative reactions from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the win but the British boxer suffered the second loss of his 28-fight professional journey.
The Champion Secures Victory in Uneventful Match
The fighter's advancement has slowed in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He started carefully, with neither fighter prepared to be aggressive in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after breaking his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to edge the more effective rounds.
The crowd's patience decreased during frequent holding, with Parker slipping to the canvas several times during grappling.
The underdog closed well, but many rounds were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor progresses, but with the caliber of power puncher Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Arthur beat Rea by split-decision in a excellent all-Manchester battle to capture the European light-heavyweight belt.
The stadium grew hushed for a deeply poignant memorial before the fight as 10 bells tolled in remembrance of local hero Ricky Hatton, who passed away 46 years old in last month.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the final chime faded, the quiet transitioned to a roar of "only one Hatton".
The fighting inside the ropes matched the emotion. Arthur was floored by a powerful punch squarely on the chin in the early round, rising shakily to his footing on the referee's count.
But the traditional red shorts of the fighter soon advanced again. From the other corner, the opponent - in competitive blue - was marked up early, heavy swelling developing under his eye as the fighters landed powerful shots.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the action rarely dropped over 12 rounds.
Arthur narrowly won the decision with official scores of 114-114, close margin and clearer margin, but both fighters were persistent and brave, everything their hero Hatton embodied.
