UK light-heavyweight Buatsi made a winning yet unimpressive debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a competitive 10-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi stated in the ringside as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Several boxing experts felt Parker, 31, deserved the victory but the British boxer suffered the second loss of his 28-match career.
Buatsi Secures Victory in Dull Match
Buatsi's progress has stalled in recent times through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a last chance - under recent support.
He started carefully, with neither fighter ready to take risks in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second appearance at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to barely take the better periods.
The crowd's patience diminished amid frequent holding, with Parker slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor advances, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a terrific local rivalry battle to win the European light heavyweight championship.
The arena grew hushed for a extremely emotional tribute prior to the bout as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the premier televised boxing event in the city since Hatton's death. As the final chime ended, the quiet became a roar of "only one Ricky Hatton".
The competition inside the ropes equaled the feeling. Arthur was knocked down by a left hook squarely on the face in the early round, standing uncertainly to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon pressed ahead again. From the other corner, Rea - in rival City blue - was marked up soon, heavy swelling forming under his eye as the duo exchanged hard punches.
The challenger, 27, connected with strong blows but Arthur, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the result with judges scorecards of 114-114, close margin and clearer margin, but each competitor were persistent and full of heart, all the qualities their hero the legend stood for.
