British light-heavyweight Buatsi earned a win yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a majority decision in a close ten-round contest at the Co-op Live Arena.
But the challenger found success, delivering effective single shots in a fight where the styles failed to mesh, with constant grabbing marring the action.
The officials had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They win," Buatsi stated in the ringside as he was met by disapproval from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in February - to claim a twentieth professional win.
Several boxing experts thought Parker, 31, deserved the victory but the British boxer experienced the second loss of his 28-bout career.
The Champion Secures Win in Dull Encounter
Buatsi's progress has slowed in recent years through contract problems and long spells of lack of fights.
Previously predicted as the next star of UK boxing, he now stands trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under fresh management.
He began cautiously, with both competitors ready to take risks in a calculated opening few 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 participating in his second appearance at light heavyweight.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who worked behind a solid defense to barely take the better periods.
The audience's tolerance decreased amid regular grabbing, with Parker going down several times during grappling.
The underdog ended stronger, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur beat Bradley Rea by split-decision in a outstanding all-Manchester contest to capture the European light heavyweight title.
The stadium grew hushed for a extremely emotional homage prior to the bout as 10 bells rang in memory of Manchester's own Hatton, who succumbed at age 46 in recently.
It was the premier televised match card in the city since Hatton's death. As the final chime faded, the stillness gave way to a shout of "only one Hatton".
The fighting inside the ropes matched the feeling. The eventual winner was sent to the canvas by a left hook directly to the face in the early round, getting up unsteadily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured early, heavy swelling appearing under his eye as the pair landed powerful shots.
Rea, twenty-seven, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor narrowly won the decision with scoring tallies of 114-114, close margin and clearer margin, but both fighters were persistent and courageous, all the qualities their hero Hatton embodied.
