UK light-heavyweight Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the approaches failed to mesh, with constant grabbing marring the action.
Two judges had it 96-94 for to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi commented in the arena as he was greeted with boos from the spectators.
The British fighter got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Various analysts thought the challenger, 31, deserved the win but the contender suffered the second loss of his 28-match career.
Buatsi Claims Victory in Dull Match
His career development has stalled in the past few years through management issues and extended periods of lack of fights.
Earlier forecast as the future of UK boxing, he now is positioned trying to realize his potential - perhaps in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter prepared to be aggressive in a cagey initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand mid-fight, was making just his second appearance at the higher weight class.
By the halfway stage, Parker had stayed in contention, creating difficulties for the favorite, who utilized a protective stance to barely take the cleaner rounds.
The spectators' acceptance diminished during regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
The underdog ended stronger, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Hatton Tribute Inspires Local Rivalry Contest
In the co-main event, Arthur overcame Bradley Rea by divided decision in a excellent all-Manchester fight to win the continental title.
The stadium grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony sounded in remembrance of local hero Hatton, who succumbed aged 46 in last month.
It was the first major televised match card in the urban center since Hatton's death. As the final chime ended, the stillness gave way to a chant of "there's just one Hatton".
The fighting within the ring equaled the emotion. Arthur was knocked down by a left hook directly to the face in the early round, rising shakily to his position on the count of eight.
But the traditional red shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was marked up soon, noticeable damage appearing under his eye as the fighters exchanged punishing blows.
Rea, 27, connected with strong blows but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity rarely dropped over 12 rounds.
The victor narrowly won the verdict with official scores of draw, narrow lead and wider gap, but the two athletes were relentless and full of heart, all the qualities their hero Hatton stood for.
