UK light heavyweight Buatsi made a winning yet unimpressive beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a majority decision in a tight ten-round bout at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a match where the styles didn't complement each other, with constant grabbing spoiling the action.
The officials had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but what defines champions? They win," Buatsi commented in the ringside as he was greeted with disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Some ringside observers thought the challenger, thirty-one, should have been awarded the decision but the British boxer suffered the second loss of his 28-fight career.
The Champion Claims Win in Dull Match
The fighter's advancement has stalled in recent times through management issues and extended periods of lack of fights.
Earlier forecast as the future of UK boxing, he now finds himself trying to realize his potential - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter prepared to be aggressive in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was participating in his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for the favorite, who operated with a protective stance to edge the more effective stanzas.
The crowd's patience decreased during frequent holding, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but multiple periods were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
The victor advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a excellent local rivalry fight to secure the continental title.
The venue became quiet for a deeply poignant homage ahead of the contest as a bell ceremony rang in memory of local hero Hatton, who passed away at age 46 in September.
It was the first major televised match card in the city since Hatton's death. As the last bell disappeared, the silence gave way to a chant of "only one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was sent to the canvas by a powerful punch squarely on the jaw in the early round, standing uncertainly to his position on the eight count.
But the traditional red equipment of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was injured soon, heavy swelling forming under his orbital area as the pair landed punishing blows.
The challenger, 27, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the pace rarely dropped over the full distance.
The victor barely secured the result with judges scorecards of 114-114, 115-113 and 115-112, but each competitor were persistent and brave, everything their inspiration the legend represented.
