UK light-heavyweight Buatsi secured a victory yet underwhelming debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a majority decision in a tight 10-round fight at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a match where the approaches didn't complement each other, with constant grabbing marring the fight.
Two judges scored it 96-94 for to Buatsi, with the third a even score.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi stated in the ringside as he was met by negative reactions from the audience.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts believed the challenger, 31, should have been awarded the win but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
Buatsi Claims Victory in Uneventful Match
His career development has plateaued in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under fresh management.
He began cautiously, with the two boxers willing to take risks in a tentative initial rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after damaging his hand mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, Parker had made it competitive, causing problems for the favorite, who utilized a solid defense to barely take the better stanzas.
The crowd's patience wore thin during frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker closed well, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still looks steep.
Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific all-Manchester contest to secure the European light heavyweight belt.
The venue fell silent for a deeply poignant tribute prior to the bout as 10 bells rang in memory of the city's native Ricky Hatton, who succumbed aged 46 in recently.
It was the first major televised match card in the location since Hatton's death. As the last bell faded, the stillness gave way to a roar of "only one Ricky Hatton".
The action within the ring equaled the feeling. The eventual winner was knocked down by a powerful punch flush on the jaw in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged early, noticeable damage forming under his orbital area as the fighters traded hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, 34, fought fire with fire with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur barely secured the result with scoring tallies of 114-114, narrow lead and clearer margin, but each competitor were determined and full of heart, everything their idol the legend stood for.
