British light-heavyweight Buatsi made a winning yet disappointing beginning to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a close ten-round fight at the Manchester venue.
But Parker landed significant shots, connecting with powerful clean blows in a contest where the approaches didn't complement each other, with frequent clinching disrupting the fight.
The scoring judges scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my finest display but what defines champions? They prevail," Buatsi said in the ring as he was greeted with negative reactions from the crowd.
The Londoner bounced back after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts felt Parker, thirty-one, deserved the decision but the British boxer experienced the second loss of his 28-bout professional journey.
The Champion Claims Triumph in Dull Encounter
Buatsi's progress has stalled in recent times through contract problems and long spells of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors ready to overcommit in a tentative early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to barely take the cleaner stanzas.
The audience's tolerance diminished during regular grabbing, with Parker going down various instances during grappling.
Parker closed well, but many rounds 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 one round.
Buatsi progresses, but with the presence of heavy hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Fuels Local Rivalry Battle
In the supporting bout, Arthur defeated Rea by divided decision in a outstanding Manchester vs Manchester fight to secure the continental belt.
The arena grew hushed for a deeply poignant tribute prior to the bout as a bell ceremony sounded in memory of the city's native Hatton, who succumbed at age 46 in September.
It was the first major televised match card in the city since the passing of Hatton. As the final chime faded, the quiet transitioned to a roar of "only one Hatton".
The action during the bout reflected the feeling. Arthur was floored by a significant blow directly to the face in the initial stage, rising shakily to his footing on the referee's count.
But the Manchester United-red attire of Arthur soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up early, significant bruising forming under his eye as the pair traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over the full distance.
Arthur edged the result with scoring tallies of draw, 115-113 and clearer margin, but the two athletes were determined and full of heart, exactly what their idol Hatton embodied.
