UK light heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a majority decision in a competitive 10-round contest at the boxing arena.
But the challenger landed significant shots, connecting with powerful individual punches in a contest where the techniques failed to mesh, with constant grabbing marring the fight.
The scoring judges judged it 96-94 to Buatsi, with the final judge a even score.
"It wasn't my greatest display but what do champions do? They prevail," Buatsi commented in the ringside as he was met by disapproval from the audience.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers believed the challenger, 31, should have been awarded the win but the Derbyshire fighter suffered the second loss of his 28-match career.
The Champion Claims Victory in Uneventful Encounter
Buatsi's progress has stalled in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now is positioned trying to realize his potential - perhaps in what feels like a ultimate opportunity - under recent support.
He began cautiously, with neither fighter ready to overcommit in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had made it competitive, making life awkward for the favorite, who worked behind a solid defense to narrowly win the cleaner stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor several times during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Contest
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a excellent Manchester vs Manchester contest to win the European light heavyweight belt.
The arena grew hushed for a extremely emotional homage prior to the bout as a bell ceremony tolled in memory of local hero Hatton, who died at age 46 in last month.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the last bell disappeared, the stillness became a roar of "there's only one Hatton".
The action inside the ropes reflected the emotion. The eventual winner was knocked down by a left hook directly to the jaw in the initial stage, rising shakily to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was marked up quickly, significant bruising forming under his eye as the duo exchanged hard punches.
Rea, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over 12 rounds.
Arthur barely secured the verdict with official scores of even score, close margin and wider gap, but the two athletes were determined and courageous, everything their idol Hatton stood for.
