UK light-heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a close 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a match where the approaches didn't complement each other, with frequent clinching spoiling the action.
The officials scored it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest display but how do champions respond? They succeed," the victor said in the arena as he was greeted with negative reactions from the crowd.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, merited the win but the contender endured the second setback of his 28-fight professional journey.
Buatsi Secures Triumph in Slow Encounter
His career development has stalled in recent times through promotional disputes and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers willing to be aggressive in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a tight guard to narrowly win the more effective stanzas.
The audience's tolerance diminished during regular grabbing, with the challenger going down various instances during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Inspires All-Manchester Fight
In the secondary fight, Arthur overcame Bradley Rea by divided decision in a terrific local rivalry battle to win the European light heavyweight title.
The arena grew hushed for a extremely emotional tribute prior to the bout as a bell ceremony tolled in remembrance of local hero Hatton, who died aged 46 in September.
It was the premier televised match card in the urban center since the passing of Hatton. As the last bell faded, the silence became a roar of "there's only one Hatton".
The competition during the bout equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the chin in the second round, rising shakily to his feet on the referee's count.
But the red-colored shorts of Arthur soon advanced again. From the other corner, the opponent - in opposing blue - was damaged quickly, significant bruising developing under his orbital area as the fighters traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the action rarely dropped over the full distance.
The victor narrowly won the result with scoring tallies of even score, close margin and 115-112, but both fighters were determined and courageous, all the qualities their inspiration the legend embodied.
