UK light-heavyweight Buatsi earned a win yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a split decision in a competitive ten-round fight at the boxing arena.
But the challenger found success, delivering effective clean blows in a match where the approaches failed to mesh, with excessive holding marring the action.
The officials judged it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They win," the victor stated in the arena as he was faced boos from the spectators.
The Londoner bounced back after his maiden career setback - an epic battle with his previous opponent in February - to earn a 20th career victory.
Some ringside observers believed the challenger, 31, deserved the win but the British boxer endured the second loss of his 28-fight career.
Buatsi Claims Victory in Slow Match
His career development has stalled in recent times through promotional disputes and extended periods of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - possibly in what seems like a last chance - under recent support.
He began cautiously, with neither fighter willing to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for Buatsi, who utilized a protective stance to narrowly win the cleaner stanzas.
The audience's tolerance decreased during frequent holding, with the challenger going down multiple occasions during close exchanges.
The underdog closed well, but many rounds were hard to judge. Nevertheless, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor progresses, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Memorial Motivates Local Rivalry Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a outstanding local rivalry battle to secure the European light-heavyweight title.
The arena fell silent for a profoundly moving homage prior to the bout as 10 bells tolled in honor of the city's native Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast match card in the location since Hatton's passing. As the last bell disappeared, the quiet transitioned to a roar of "only one Hatton".
The competition within the ring matched the feeling. The eventual winner was sent to the canvas by a powerful punch directly to the chin in the second round, rising shakily to his footing on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up soon, heavy swelling appearing under his eye as the duo exchanged hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the verdict with official scores of 114-114, narrow lead and 115-112, but each competitor were persistent and full of heart, everything their hero Hatton embodied.
