British light-heavyweight Buatsi secured a victory yet underwhelming debut to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round bout at the boxing arena.
But Parker found success, connecting with powerful clean blows in a contest where the approaches failed to mesh, with frequent clinching disrupting the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my best showing but what defines champions? They succeed," Buatsi stated in the ring as he was greeted with boos from the crowd.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in February - to secure a 20th career victory.
Various analysts felt Parker, 31, deserved the win but the contender endured the second defeat of his 28-bout professional journey.
Buatsi Claims Victory in Uneventful Encounter
Buatsi's progress has plateaued in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers prepared to be aggressive in a calculated opening few rounds.
Parker, whose sole prior loss came at super-middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at light-heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for Buatsi, who utilized a protective stance to narrowly win the more effective periods.
The spectators' acceptance diminished during frequent holding, with Parker going down various instances during grappling.
The underdog closed well, but several stanzas were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Motivates Local Rivalry Fight
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester contest to secure the European light-heavyweight championship.
The arena became quiet for a profoundly moving homage before the fight as 10 bells tolled in honor of Manchester's own Hatton, who died 46 years old in recently.
It was the premier televised match card in the location since the passing of Hatton. As the concluding sound disappeared, the stillness became a shout of "there's only one Hatton".
The fighting within the ring reflected the sentiment. Arthur was knocked down by a powerful punch directly to the jaw in the early round, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was marked up early, heavy swelling forming under his eye as the duo landed powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the result with scoring tallies of draw, close margin and 115-112, but the two athletes were relentless and brave, all the qualities their hero the legend stood for.
