UK light-heavyweight Buatsi secured a victory yet underwhelming debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a tight ten-round bout at the Manchester venue.
But the challenger landed significant shots, connecting with powerful individual punches in a fight where the styles never quite clicked, with excessive holding disrupting the fight.
The officials judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi stated in the ringside as he was faced negative reactions from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Some ringside observers believed Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second defeat of his 28-bout career.
The Champion Claims Victory in Slow Match
His career development has stalled in recent times through promotional disputes and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - possibly in what feels like a last chance - under recent support.
He started carefully, with both competitors ready to be aggressive in a cagey initial rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second appearance at the higher weight class.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who utilized a tight guard to narrowly win the more effective rounds.
The spectators' acceptance decreased amid frequent holding, with Parker going down several times during close exchanges.
Parker closed well, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the caliber of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates All-Manchester Battle
In the secondary fight, Arthur defeated Rea by split-decision in a outstanding local rivalry contest to secure the European light-heavyweight championship.
The arena became quiet for a extremely emotional homage before the fight as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast boxing event in the urban center since Hatton's death. As the final chime ended, the stillness gave way to a roar of "only one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was sent to the canvas by a significant blow squarely on the face in the early round, getting up unsteadily to his footing on the referee's count.
But the traditional red attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up early, heavy swelling developing under his face as the pair traded powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor barely secured the result with scoring tallies of even score, narrow lead and 115-112, but both fighters were determined and brave, exactly what their idol Hatton embodied.
