British light heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a close ten-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a match where the techniques failed to mesh, with frequent clinching marring the fight.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my finest performance but what defines champions? They prevail," the victor said in the ringside as he was greeted with negative reactions from the audience.
The Londoner bounced back after his first professional defeat - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers felt Parker, 31, merited the victory but the British boxer suffered the second defeat of his 28-bout career.
Buatsi Earns Win in Slow Match
His career development has stalled in recent years through management issues and long spells of lack of fights.
Once tipped as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what feels like a last chance - under new promotional backing.
He opened tentatively, with the two boxers prepared to take risks in a cagey early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for the favorite, who utilized a solid defense to edge the better stanzas.
The audience's tolerance wore thin amid frequent holding, with the challenger going down several times during clinches.
Parker ended stronger, but multiple periods were challenging to assess. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Hatton Tribute Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Bradley Rea by divided decision in a terrific local rivalry battle to capture the European light heavyweight belt.
The stadium became quiet for a profoundly moving homage prior to the bout as 10 bells sounded in remembrance of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the final chime ended, the silence became a shout of "there's just one Hatton".
The action during the bout matched the sentiment. The eventual winner was knocked down by a significant blow flush on the face in the initial stage, standing uncertainly to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, Rea - in opposing blue - was marked up early, noticeable damage forming under his face as the fighters exchanged punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the intensity rarely dropped over twelve rounds.
Arthur narrowly won the result with judges scorecards of even score, close margin and wider gap, but each competitor were persistent and brave, exactly what their inspiration the legend stood for.
