UK light heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a judges' verdict in a close 10-round bout at the Co-op Live Arena.
But the challenger found success, connecting with powerful single shots in a fight where the techniques didn't complement each other, with frequent clinching disrupting the fight.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what defines champions? They succeed," the victor commented in the ringside as he was met by boos from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to secure a 20th career victory.
Several boxing experts believed the challenger, 31, deserved the victory but the contender endured the second defeat of his 28-fight career.
The Champion Secures Triumph in Uneventful Affair
His career development has slowed in the past few years through management issues and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under recent support.
He started carefully, with neither fighter ready to be aggressive in a cagey initial rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to barely take the better rounds.
The audience's tolerance wore thin amid regular grabbing, with the challenger falling to the floor multiple occasions during clinches.
Parker ended stronger, but multiple periods were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
Buatsi advances, but with the likes of hard hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Homage Inspires Manchester Derby Contest
In the co-main event, Lyndon Arthur beat Rea by close verdict in a terrific all-Manchester fight to win the European light heavyweight championship.
The stadium became quiet for a extremely emotional tribute prior to the bout as a bell ceremony tolled in remembrance of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised match card in the location since Hatton's passing. As the concluding sound disappeared, the quiet became a shout of "only one Ricky Hatton".
The fighting inside the ropes reflected the sentiment. Arthur was sent to the canvas by a left hook flush on the chin in the initial stage, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of the fighter soon advanced again. On the opposite side, Rea - in rival City blue - was damaged soon, heavy swelling appearing under his eye as the duo exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and 115-112, but each competitor were persistent and full of heart, all the qualities their inspiration the legend embodied.
