British light-heavyweight Buatsi secured a victory yet disappointing beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a competitive 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a contest where the approaches failed to mesh, with constant grabbing spoiling the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi stated in the ringside as he was greeted with negative reactions from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Various analysts thought Parker, thirty-one, deserved the decision but the contender experienced the second loss of his 28-match career.
Buatsi Secures Victory in Slow Match
Buatsi's progress has slowed in the past few years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to overcommit in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a tight guard to narrowly win the more effective periods.
The spectators' acceptance diminished during constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the presence of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - on this evidence - still seems difficult.
Hatton Tribute Fuels All-Manchester Battle
In the co-main event, Arthur defeated Bradley Rea by divided decision in a outstanding local rivalry contest to capture the European light-heavyweight championship.
The arena fell silent for a extremely emotional memorial prior to the bout as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who died 46 years old in recently.
It was the first major televised boxing event in the location since Hatton's passing. As the concluding sound faded, the silence gave way to a roar of "only one Ricky Hatton".
The competition during the bout reflected the sentiment. Arthur was sent to the canvas by a left hook squarely on the chin in the second round, getting up unsteadily to his feet on the eight count.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up quickly, significant bruising developing under his face as the duo landed powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
The victor barely secured the result with official scores of draw, narrow lead and 115-112, but the two athletes were relentless and full of heart, exactly what their inspiration the legend stood for.
