British light-heavyweight Buatsi secured a victory yet unimpressive start to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a close 10-round fight at the boxing arena.
But Parker found success, delivering effective clean blows in a fight where the approaches failed to mesh, with excessive holding spoiling the contest.
The scoring judges had it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi commented in the arena as he was faced disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts thought the challenger, thirty-one, deserved the victory but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
Buatsi Earns Victory in Slow Match
His career development has slowed in recent times through promotional disputes and long spells of lack of fights.
Previously predicted as the future of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a last chance - under new promotional backing.
He opened tentatively, with neither fighter prepared to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against John Ryder in 2022 after suffering a hand injury during the bout, was making just his second appearance at light heavyweight.
By the halfway stage, Parker had stayed in contention, making life awkward for Buatsi, who operated with a tight guard to edge the cleaner rounds.
The crowd's patience decreased amid regular grabbing, with Parker falling to the floor various instances during clinches.
Parker finished the stronger, but several stanzas were difficult to score. Although, previous titleholder Carl Frampton - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just one round.
The victor advances, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester battle to win the European light heavyweight title.
The venue became quiet for a profoundly moving homage ahead of the contest as a bell ceremony sounded in remembrance of local hero Hatton, who succumbed at age 46 in September.
It was the premier televised fight night in the location since Hatton's death. As the last bell disappeared, the silence became a shout of "there's just one Ricky Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was knocked down by a powerful punch flush on the chin in the second round, standing uncertainly to his footing on the count of eight.
But the traditional red attire of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was damaged soon, heavy swelling developing under his orbital area as the pair landed hard punches.
The challenger, 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 narrowly won the verdict with judges scorecards of draw, close margin and 115-112, but each competitor were determined and courageous, everything their inspiration the legend represented.
