UK light-heavyweight Buatsi secured a victory yet disappointing debut to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's activity level seemingly secured him a majority decision in a tight ten-round bout at the boxing arena.
But Parker found success, delivering effective individual punches in a match where the techniques didn't complement each other, with constant grabbing spoiling the action.
The officials scored it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but what do champions do? They win," Buatsi commented in the ring as he was greeted with negative reactions from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Several boxing experts believed the challenger, thirty-one, deserved the victory but the British boxer suffered the second setback of his 28-bout career.
The Champion Claims Win in Dull Encounter
Buatsi's progress has slowed in recent times through promotional disputes and long spells of lack of fights.
Once tipped as the next star 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 the two boxers ready to overcommit in a cagey early stages.
Parker, whose sole prior loss came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second bout at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who worked behind a protective stance to edge the better stanzas.
The audience's tolerance wore thin amid frequent holding, with Parker falling to the floor various instances during grappling.
Parker closed well, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of hard hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur beat Bradley Rea by split-decision in a terrific local rivalry battle to secure the European light-heavyweight belt.
The venue fell silent for a profoundly moving homage ahead of the contest as a bell ceremony rang in remembrance of Manchester's own Ricky Hatton, who died aged 46 in last month.
It was the first major televised fight night in the city since the passing of Hatton. As the concluding sound faded, the quiet gave way to a roar of "there's only one Hatton".
The competition during the bout matched the feeling. The eventual winner was floored by a powerful punch flush on the jaw in the initial stage, standing uncertainly to his footing on the count of eight.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, Rea - in rival City blue - was injured quickly, noticeable damage developing under his eye as the pair traded punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity rarely dropped over twelve rounds.
The victor barely secured the decision with scoring tallies of draw, narrow lead and 115-112, but both fighters were relentless and full of heart, everything their idol Hatton embodied.
