UK light heavyweight Buatsi secured a victory yet unimpressive debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a close 10-round fight at the Co-op Live Arena.
But Parker had his moments, landing some telling single shots in a match where the styles failed to mesh, with frequent clinching disrupting the fight.
The officials scored it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest performance but what defines champions? They win," Buatsi commented in the ring as he was faced negative reactions from the crowd.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Various analysts felt the challenger, thirty-one, merited the decision but the British boxer suffered the second loss of his 28-match professional journey.
The Champion Secures Triumph in Uneventful Match
His career development has slowed in recent times through management issues and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter prepared to be aggressive in a calculated initial rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who utilized a protective stance to edge the better periods.
The crowd's patience diminished because of frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. Although, previous titleholder the boxing analyst - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Memorial Motivates Manchester Derby Battle
In the supporting bout, Arthur beat Bradley Rea by split-decision in a outstanding Manchester vs Manchester fight to capture the European light-heavyweight title.
The stadium became quiet for a extremely emotional memorial before the fight as 10 bells tolled in memory of local hero Hatton, who passed away aged 46 in September.
It was the initial significant broadcast match card in the city since Hatton's passing. As the last bell faded, the quiet became a chant of "there's only one Ricky Hatton".
The fighting inside the ropes matched the emotion. Arthur was floored by a significant blow directly to the chin in the second round, rising shakily to his position on the eight count.
But the Manchester United-red equipment of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was damaged early, heavy swelling forming under his orbital area as the fighters landed powerful shots.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of even score, 115-113 and 115-112, but each competitor were relentless and full of heart, exactly what their inspiration Hatton represented.
