British light-heavyweight Buatsi secured a victory yet underwhelming debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a tight ten-round fight at the boxing arena.
But the challenger landed significant shots, delivering effective individual punches in a fight where the styles failed to mesh, with excessive holding spoiling the fight.
The officials had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi said in the ring as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to secure a 20th pro success.
Some ringside observers believed the challenger, 31, should have been awarded the victory but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
Buatsi Claims Victory in Uneventful Match
His career development has stalled in the past few years through promotional disputes and long spells of lack of fights.
Once tipped as the next star of the British fight scene, he now stands trying to achieve expectations - perhaps in what seems like a last chance - under recent support.
He started carefully, with neither fighter willing to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who operated with a solid defense to narrowly win the cleaner stanzas.
The crowd's patience decreased because of regular grabbing, with Parker falling to the floor multiple occasions during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. However, former world champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the presence of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Hatton Homage Motivates Manchester Derby Fight
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to secure the continental title.
The stadium fell silent for a extremely emotional memorial before the fight as 10 bells sounded in honor of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the first major televised fight night in the location since the passing of Hatton. As the concluding sound ended, the quiet became a shout of "there's just one Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a powerful punch squarely on the jaw in the second round, getting up unsteadily to his footing on the eight count.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was marked up early, heavy swelling forming under his eye as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over the full distance.
The victor narrowly won the decision with scoring tallies of 114-114, close margin and 115-112, but each competitor were relentless and full of heart, all the qualities their hero the legend embodied.
