British light heavyweight Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close ten-round fight at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a match where the techniques didn't complement each other, with constant grabbing disrupting the fight.
Two judges judged it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi commented in the arena as he was greeted with boos from the crowd.
The Londoner returned to winning ways after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th pro success.
Various analysts thought the challenger, thirty-one, merited the win but the contender experienced the second loss of his 28-match professional journey.
Buatsi Secures Triumph in Dull Encounter
The fighter's advancement has plateaued in recent years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers willing to take risks in a cagey early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who operated with a tight guard to edge the more effective stanzas.
The audience's tolerance diminished because of constant clinching, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but several stanzas were hard to judge. However, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor advances, but with the likes of hard hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Homage Fuels Manchester Derby Fight
In the co-main event, Arthur beat Rea by divided decision in a outstanding local rivalry battle to win the European light-heavyweight championship.
The stadium became quiet for a extremely emotional memorial prior to the bout as a bell ceremony tolled in remembrance of local hero Hatton, who died at age 46 in September.
It was the first major televised fight night in the urban center since Hatton's death. As the final chime faded, the quiet transitioned to a chant of "there's only one Ricky Hatton".
The fighting during the bout reflected the emotion. Arthur was sent to the canvas by a significant blow squarely on the jaw in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored attire of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was damaged quickly, significant bruising developing under his face as the pair traded powerful shots.
The challenger, twenty-seven, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the action hardly diminished over the full distance.
The victor barely secured the result with judges scorecards of even score, close margin and wider gap, but each competitor were persistent and full of heart, all the qualities their idol Hatton represented.
