UK light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But the challenger landed significant shots, landing some telling clean blows in a contest where the styles didn't complement each other, with constant grabbing marring the fight.
The scoring judges judged it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my greatest showing but what do champions do? They win," Buatsi stated in the arena as he was greeted with disapproval from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Several boxing experts believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second defeat of his 28-match professional journey.
Buatsi Claims Win in Uneventful Match
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of lack of fights.
Earlier forecast as the future of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter ready to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in 2022 after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the halfway stage, the underdog had kept it close, creating difficulties for the favorite, who utilized a solid defense to narrowly win the cleaner stanzas.
The crowd's patience decreased because of frequent holding, with the challenger going down multiple occasions during close exchanges.
The underdog closed well, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur overcame Rea by split-decision in a terrific all-Manchester contest to secure the continental championship.
The venue became quiet for a extremely emotional tribute prior to the bout as ten bells tolled in honor of Manchester's own Hatton, who succumbed at age 46 in last month.
It was the first major televised match card in the location since Hatton's passing. As the last bell ended, the silence became a roar of "there's only one Ricky Hatton".
The fighting during the bout reflected the sentiment. The eventual winner was sent to the canvas by a significant blow squarely on the chin in the early round, standing uncertainly to his footing on the eight count.
But the red-colored equipment of Arthur soon came forward again. Across the ring, Rea - in opposing blue - was injured early, significant bruising forming under his face as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor barely secured the verdict with scoring tallies of 114-114, 115-113 and clearer margin, but the two athletes were determined and courageous, everything their idol Hatton embodied.
