British light heavyweight Buatsi secured a victory yet unimpressive beginning to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a close ten-round fight at the Co-op Live Arena.
But Parker had his moments, delivering effective individual punches in a match where the techniques never quite clicked, with frequent clinching spoiling the contest.
The officials had it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best display but how do champions respond? They succeed," the victor said in the arena as he was greeted with negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers believed the challenger, 31, merited the win but the contender endured the second setback of his 28-match career.
Buatsi Earns Triumph in Dull Affair
His career development has plateaued in the past few years through promotional disputes and considerable time of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with neither fighter willing to overcommit in a tentative 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 making just his second bout at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to edge the better periods.
The audience's tolerance diminished amid constant clinching, with the challenger going down various instances during close exchanges.
The underdog closed well, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of hard hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Motivates All-Manchester Battle
In the co-main event, Arthur defeated Bradley Rea by split-decision in a terrific all-Manchester contest to capture the European light heavyweight belt.
The stadium fell silent for a profoundly moving homage ahead of the contest as ten bells sounded in remembrance of Manchester's own Ricky 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 final chime ended, the silence transitioned to a shout of "there's just one Hatton".
The action within the ring reflected the emotion. The eventual winner was sent to the canvas by a powerful punch flush on the face in the early round, standing uncertainly to his feet on the referee's count.
But the traditional red equipment of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was injured quickly, heavy swelling appearing under his orbital area as the pair landed hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace seldom decreased over twelve rounds.
Arthur narrowly won the decision with scoring tallies of draw, close margin and 115-112, but each competitor were determined and courageous, everything their inspiration the legend represented.
