British light-heavyweight Buatsi secured a victory yet unimpressive beginning to his career under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a split decision in a competitive 10-round contest at the Co-op Live Arena.
But the challenger found success, connecting with powerful individual punches in a fight where the styles didn't complement each other, with constant grabbing marring the fight.
The officials scored it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but how do champions respond? They succeed," the victor stated in the ring as he was faced disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers felt the challenger, 31, deserved the decision but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
The Champion Secures Win in Dull Affair
Buatsi's progress has stalled in recent times through promotional disputes and long spells of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now stands trying to achieve expectations - perhaps in what feels like a last chance - under recent support.
He began cautiously, with the two boxers prepared to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second fight at the higher weight class.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who operated with a protective stance to narrowly win the cleaner periods.
The spectators' acceptance decreased during frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
The underdog closed well, but many rounds were hard to judge. However, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Tribute Inspires Local Rivalry Contest
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a excellent Manchester vs Manchester battle to capture the European light heavyweight belt.
The stadium became quiet for a profoundly moving tribute prior to the bout as a bell ceremony rang in remembrance of the city's native Hatton, who succumbed 46 years old in September.
It was the premier televised boxing event in the city since the passing of Hatton. As the concluding sound faded, the stillness became a chant of "only one Hatton".
The action within the ring matched the emotion. The eventual winner was sent to the canvas by a left hook directly to the chin in the early round, getting up unsteadily to his position on the referee's count.
But the red-colored shorts of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was marked up soon, significant bruising forming under his orbital area as the duo traded hard punches.
The challenger, 27, connected with strong blows but the champion, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over 12 rounds.
Arthur narrowly won the result with official scores of draw, 115-113 and clearer margin, but both fighters were persistent and full of heart, all the qualities their hero Hatton embodied.
