British light-heavyweight Buatsi made a winning yet underwhelming debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive ten-round bout at the boxing arena.
But Parker landed significant shots, delivering effective clean blows in a fight where the styles failed to mesh, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 to the winner, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi commented in the ringside as he was faced disapproval from the crowd.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts believed the challenger, 31, merited the victory but the contender experienced the second loss of his 28-match career.
Buatsi Earns Victory in Dull Match
His career development has plateaued in recent years through management issues and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now is positioned trying to realize his potential - perhaps in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors willing to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was participating in his second appearance at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who utilized a tight guard to edge the better rounds.
The audience's tolerance wore thin because of constant clinching, with the challenger going down several times during clinches.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, former world champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a outstanding all-Manchester fight to secure the continental championship.
The stadium became quiet for a extremely emotional homage ahead of the contest as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the city since the passing of Hatton. As the last bell faded, the silence transitioned to a roar of "there's just one Hatton".
The fighting inside the ropes matched the sentiment. Arthur was floored by a powerful punch squarely on the chin in the initial stage, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was damaged early, significant bruising developing under his orbital area as the duo landed hard punches.
Rea, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
The victor edged the decision with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were persistent and full of heart, everything their idol Hatton embodied.
