UK light-heavyweight Buatsi earned a win yet disappointing start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a tight 10-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling individual punches in a fight where the techniques failed to mesh, with frequent clinching marring the contest.
The scoring judges judged it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest performance but how do champions respond? They win," the victor 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 epic battle with his previous opponent in last winter - to earn a 20th pro success.
Several boxing experts thought Parker, 31, merited the decision but the contender endured the second defeat of his 28-bout career.
The Champion Claims Triumph in Dull Affair
His career development has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a final roll of the dice - under fresh management.
He started carefully, with both competitors prepared to overcommit in a calculated early stages.
Parker, whose sole prior loss came at super-middleweight against his former opponent 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, Parker had kept it close, creating difficulties for the favorite, who operated with a protective stance to edge the cleaner stanzas.
The spectators' acceptance decreased during frequent holding, with the challenger falling to the floor multiple occasions during close exchanges.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of power puncher David Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Hatton Homage Inspires Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester fight to secure the European light-heavyweight title.
The venue grew hushed for a extremely emotional memorial prior to the bout as 10 bells tolled in memory of the city's native Hatton, who died aged 46 in recently.
It was the first major televised match card in the city since Hatton's death. As the final chime faded, the stillness gave way to a shout of "only one Ricky Hatton".
The competition inside the ropes matched the feeling. Arthur was knocked down by a powerful punch directly to the jaw in the initial stage, standing uncertainly to his footing on the eight count.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, the opponent - in opposing blue - was marked up early, heavy swelling appearing under his face as the duo landed powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
The victor narrowly won the verdict with official scores of even score, close margin and clearer margin, but each competitor were persistent and full of heart, all the qualities their hero Hatton embodied.
