British light heavyweight Buatsi secured a victory yet disappointing beginning to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a split decision in a close ten-round bout at the Manchester venue.
But Parker found success, connecting with powerful single shots in a fight where the styles didn't complement each other, with frequent clinching marring the contest.
The scoring judges had it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my best performance but what defines champions? They prevail," Buatsi stated in the ringside as he was met by negative reactions from the crowd.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th career victory.
Some ringside observers believed the challenger, 31, merited the decision but the contender endured the second loss of his 28-fight professional journey.
Buatsi Earns Triumph in Uneventful Match
Buatsi's progress has slowed in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - possibly in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with neither fighter ready to overcommit in a cagey early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who operated with a protective stance to edge the better periods.
The crowd's patience decreased because of regular grabbing, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Although, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Memorial Motivates Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding local rivalry contest to capture the European light-heavyweight championship.
The stadium fell silent for a deeply poignant homage ahead of the contest as a bell ceremony tolled in honor of local hero Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the urban center since Hatton's passing. As the last bell ended, the quiet gave way to a roar of "there's just one Hatton".
The competition within the ring equaled the sentiment. The eventual winner was sent to the canvas by a significant blow squarely on the chin in the early round, rising shakily to his feet on the eight count.
But the traditional red attire of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling forming under his orbital area as the fighters exchanged powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with powerful upward punches as the intensity seldom decreased over twelve rounds.
The victor narrowly won the result with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were relentless and courageous, exactly what their inspiration Hatton represented.
