UK light-heavyweight Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a tight 10-round bout at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a match where the techniques never quite clicked, with excessive holding disrupting the contest.
Two judges scored it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest performance but what defines champions? They succeed," Buatsi said in the ringside as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers felt the challenger, thirty-one, deserved the victory but the Derbyshire fighter experienced the second setback of his 28-match career.
The Champion Claims Win in Slow Match
The fighter's advancement has stalled in recent times through management issues and long spells of inactivity.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - possibly in what seems like a last chance - under recent support.
He started carefully, with the two boxers ready to take risks in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second appearance at the higher weight class.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who utilized a protective stance to narrowly win the better rounds.
The spectators' acceptance wore thin amid frequent holding, with the challenger going down several times during close exchanges.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, scoring for Buatsi just one round.
The victor moves on, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a excellent local rivalry battle to capture the European light-heavyweight championship.
The arena grew hushed for a deeply poignant memorial before the fight as a bell ceremony tolled in honor of Manchester's own Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the final chime ended, the stillness became a shout of "only one Ricky Hatton".
The action within the ring matched the emotion. Arthur was knocked down by a powerful punch directly to the chin in the initial stage, rising shakily to his feet on the count of eight.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was damaged soon, noticeable damage forming under his face as the fighters traded powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, fought fire with fire with stinging uppercuts as the action rarely dropped over twelve rounds.
Arthur edged the verdict with scoring tallies of even score, 115-113 and wider gap, but both fighters were persistent and brave, all the qualities their hero Hatton represented.
