UK light-heavyweight Buatsi earned a win yet disappointing start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a tight 10-round contest at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a contest where the approaches never quite clicked, with constant grabbing disrupting the fight.
Two judges scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best performance but how do champions respond? They win," Buatsi commented in the arena as he was met by negative reactions from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the win but the British boxer suffered the second setback of his 28-match career.
The Champion Earns Triumph in Dull Match
The fighter's advancement has plateaued in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of UK boxing, he now stands trying to achieve expectations - possibly in what appears to be a last chance - under new promotional backing.
He started carefully, with the two boxers ready to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was making just his second appearance at light-heavyweight.
By the halfway stage, the underdog had stayed in contention, making life awkward for Buatsi, who worked behind a tight guard to barely take the cleaner stanzas.
The audience's tolerance diminished during frequent holding, with the challenger going down multiple occasions during close exchanges.
Parker closed well, but many rounds were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the co-main event, Arthur overcame Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light heavyweight title.
The venue became quiet for a profoundly moving memorial ahead of the contest as 10 bells tolled in memory of the city's native Hatton, who died 46 years old in recently.
It was the first major televised fight night in the location since Hatton's death. As the concluding sound disappeared, the silence became a shout of "there's only one Hatton".
The action during the bout matched the emotion. The eventual winner was sent to the canvas by a powerful punch squarely on the face in the initial stage, getting up unsteadily to his position on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured quickly, heavy swelling appearing under his eye as the duo traded punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor edged the result with scoring tallies of even score, narrow lead and 115-112, but each competitor were determined and brave, everything their inspiration the legend represented.
