UK light-heavyweight Buatsi secured a victory yet underwhelming start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive ten-round fight at the Manchester venue.
But the challenger found success, landing some telling single shots in a match where the approaches didn't complement each other, with excessive holding marring the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best performance but what do champions do? They prevail," Buatsi said in the arena as he was met by disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts thought Parker, thirty-one, deserved the victory but the British boxer suffered the second setback of his 28-bout professional journey.
Buatsi Secures Victory in Slow Affair
Buatsi's progress has slowed in recent years through management issues and long spells of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to achieve expectations - maybe in what appears to be a last chance - under recent support.
He opened tentatively, with neither fighter prepared to be aggressive in a tentative opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for the favorite, who operated with a solid defense to barely take the better stanzas.
The crowd's patience diminished during regular grabbing, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a excellent local rivalry battle to capture the European light heavyweight championship.
The stadium grew hushed for a deeply poignant tribute prior to the bout as ten bells tolled in remembrance of the city's native Ricky Hatton, who died aged 46 in September.
It was the premier televised fight night in the location since the passing of Hatton. As the last bell ended, the quiet became a shout of "only one Ricky Hatton".
The fighting during the bout reflected the emotion. Arthur was sent to the canvas by a powerful punch directly to the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the Manchester United-red equipment of the fighter soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was damaged quickly, noticeable damage forming under his face as the fighters exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the intensity rarely dropped over the full distance.
The victor edged the result with judges scorecards of 114-114, 115-113 and clearer margin, but each competitor were determined and courageous, all the qualities their inspiration the legend stood for.
