UK light-heavyweight Buatsi made a winning yet disappointing debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker found success, landing some telling individual punches in a contest where the approaches didn't complement each other, with excessive holding marring the fight.
Two judges scored it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but what defines champions? They prevail," Buatsi stated in the ringside as he was met by disapproval from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to claim a 20th pro success.
Various analysts believed the challenger, 31, merited the win but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
Buatsi Earns Win in Slow Encounter
Buatsi's progress has slowed in recent times through contract problems and considerable time of lack of fights.
Previously predicted as the next star of British boxing, he now finds himself trying to fulfil that early promise - maybe in what feels like a last chance - under new promotional backing.
He opened tentatively, with both competitors prepared to be aggressive in a cagey initial rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was competing in only his second fight at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who operated with a tight guard to barely take the cleaner stanzas.
The crowd's patience diminished because of regular grabbing, with Parker falling to the floor several times during close exchanges.
The underdog ended stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Hatton Memorial Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Rea by close verdict in a outstanding all-Manchester contest to win the continental championship.
The stadium fell silent for a profoundly moving homage ahead of the contest as ten bells sounded in remembrance of Manchester's own Hatton, who died aged 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's passing. As the concluding sound disappeared, the silence gave way to a chant of "only one Ricky Hatton".
The fighting within the ring equaled the feeling. The eventual winner was knocked down by a significant blow directly to the face in the initial stage, getting up unsteadily to his position on the referee's count.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged early, significant bruising forming under his face as the pair landed hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the intensity rarely dropped over twelve rounds.
The victor narrowly won the verdict with official scores of draw, narrow lead and clearer margin, but each competitor were relentless and brave, exactly what their inspiration the legend embodied.
