British light heavyweight Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive ten-round contest at the boxing arena.
But Parker had his moments, connecting with powerful individual punches in a contest where the styles failed to mesh, with frequent clinching disrupting the action.
The scoring judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my greatest display but what do champions do? They win," the victor stated in the ringside as he was greeted with boos from the crowd.
The British fighter got back to winning after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers thought Parker, 31, should have been awarded the win but the contender experienced the second defeat of his 28-fight professional journey.
The Champion Secures Triumph in Slow Affair
Buatsi's progress has stalled in recent years through contract problems and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to achieve expectations - possibly in what seems like a last chance - under new promotional backing.
He opened tentatively, with neither fighter ready to be aggressive in a tentative initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who operated with a solid defense to edge the more effective rounds.
The spectators' acceptance decreased amid frequent holding, with Parker falling to the floor various instances during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. Nevertheless, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Hatton Homage Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur defeated Rea by divided decision in a excellent Manchester vs Manchester contest to secure the European light heavyweight belt.
The venue grew hushed for a extremely emotional tribute ahead of the contest as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who passed away aged 46 in recently.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the final chime faded, the stillness transitioned to a shout of "only one Hatton".
The competition inside the ropes reflected the emotion. Arthur was knocked down by a significant blow directly to the chin in the initial stage, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was damaged quickly, noticeable damage developing under his face as the duo traded hard punches.
The challenger, 27, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur barely secured the decision with scoring tallies of draw, narrow lead and 115-112, but each competitor were determined and brave, everything their hero Hatton embodied.
