British light-heavyweight Buatsi made a winning yet disappointing beginning to his career under new promoters 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 competitive 10-round contest at the boxing arena.
But Parker found success, landing some telling clean blows in a fight where the techniques didn't complement each other, with frequent clinching marring the action.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," the victor said in the ringside as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Some ringside observers believed Parker, thirty-one, deserved the decision but the British boxer suffered the second setback of his 28-match career.
The Champion Claims Triumph in Slow Affair
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - possibly in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with the two boxers willing to be aggressive in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class 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 middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to barely take the more effective periods.
The crowd's patience diminished because of frequent holding, with Parker going down several times during clinches.
Parker closed well, but many rounds were hard to judge. Although, former world champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Homage Inspires Manchester Derby Battle
In the secondary fight, Arthur beat Rea by divided decision in a terrific local rivalry contest to capture the continental title.
The venue grew hushed for a extremely emotional memorial ahead of the contest as ten bells tolled in remembrance of the city's native Hatton, who passed away 46 years old in last month.
It was the first major televised boxing event in the location since Hatton's passing. As the final chime disappeared, the stillness transitioned to a shout of "only one Ricky Hatton".
The action during the bout matched the sentiment. Arthur was sent to the canvas by a significant blow flush on the chin in the initial stage, standing uncertainly to his footing on the referee's count.
But the red-colored shorts of Arthur soon came forward again. Across the ring, Rea - in competitive blue - was damaged quickly, significant bruising developing under his eye as the duo traded powerful shots.
The challenger, 27, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the decision with official scores of even score, narrow lead and wider gap, but each competitor were persistent and full of heart, all the qualities their inspiration the legend represented.
