British light-heavyweight Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight 10-round contest at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a contest where the approaches never quite clicked, with frequent clinching marring the fight.
The officials judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They succeed," Buatsi commented in the arena as he was faced negative reactions from the audience.
The Londoner returned to winning ways after his first professional defeat - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Various analysts felt the challenger, thirty-one, merited the victory but the contender experienced the second setback of his 28-bout professional journey.
The Champion Claims Victory in Slow Match
Buatsi's progress has slowed in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now stands trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with neither fighter prepared to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in 2022 after suffering a hand injury during the bout, was making just his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for Buatsi, who operated with a tight guard to edge the better rounds.
The spectators' acceptance decreased during frequent holding, with the challenger going down multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Hatton Homage Motivates Local Rivalry Battle
In the supporting bout, Arthur defeated Bradley Rea by split-decision in a terrific local rivalry contest to capture the continental title.
The stadium grew hushed for a deeply poignant tribute prior to the bout as a bell ceremony rang in remembrance of Manchester's own Hatton, who passed away aged 46 in last month.
It was the first major televised match card in the urban center since the passing of Hatton. As the last bell faded, the quiet became a chant of "only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was sent to the canvas by a left hook directly to the jaw in the early round, getting up unsteadily to his footing on the count of eight.
But the Manchester United-red equipment of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was injured quickly, significant bruising developing under his face as the pair traded punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over twelve rounds.
The victor narrowly won the verdict with scoring tallies of draw, 115-113 and wider gap, but the two athletes were persistent and full of heart, exactly what their idol the legend embodied.
