UK light heavyweight Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close 10-round bout at the boxing arena.
But the challenger found success, landing some telling single shots in a fight where the approaches failed to mesh, with excessive holding marring the contest.
Two judges scored it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but what do champions do? They prevail," the victor stated in the arena as he was faced boos from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought the challenger, 31, deserved the win but the Derbyshire fighter suffered the second loss of his 28-bout career.
The Champion Secures Win in Slow Match
His career development has slowed in the past few years through contract problems and long spells of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to achieve expectations - possibly in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers prepared to overcommit in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the middle rounds, the underdog had stayed in contention, causing problems for the favorite, who utilized a protective stance to edge the more effective stanzas.
The audience's tolerance wore thin because of regular grabbing, with Parker going down various instances during grappling.
The underdog closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the likes of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the co-main event, Arthur defeated Bradley Rea by close verdict in a excellent all-Manchester battle to secure the European light heavyweight title.
The venue grew hushed for a profoundly moving tribute prior to the bout as a bell ceremony rang in honor of local hero Hatton, who passed away at age 46 in recently.
It was the premier televised boxing event in the location since Hatton's death. As the last bell disappeared, the silence gave way to a chant of "there's only one Ricky Hatton".
The fighting within the ring equaled the feeling. Arthur was floored by a powerful punch flush on the jaw in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was injured early, heavy swelling appearing under his orbital area as the fighters landed punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity hardly diminished over the full distance.
Arthur barely secured the result with scoring tallies of 114-114, 115-113 and wider gap, but the two athletes were relentless and full of heart, everything their inspiration the legend embodied.
