UK light heavyweight Buatsi earned a win yet disappointing debut to life under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a competitive 10-round contest at the Manchester venue.
But the challenger landed significant shots, delivering effective single shots in a contest where the approaches failed to mesh, with frequent clinching disrupting the action.
The scoring judges scored it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest performance but what do champions do? They succeed," the victor stated in the ring as he was greeted with disapproval from the audience.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to claim a 20th career victory.
Various analysts felt the challenger, 31, merited the win but the Derbyshire fighter suffered the second setback of his 28-bout professional journey.
The Champion Secures Win in Uneventful Affair
The fighter's advancement has stalled in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the next star 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 started carefully, with the two boxers willing to be aggressive in a cagey early stages.
The challenger, whose single earlier setback came at super-middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second bout at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a tight guard to edge the cleaner stanzas.
The spectators' acceptance wore thin because of constant clinching, with Parker slipping to the canvas various instances during grappling.
Parker ended stronger, but multiple periods were challenging to assess. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Fight
In the supporting bout, Arthur overcame Rea by close verdict in a terrific local rivalry battle to capture the European light heavyweight championship.
The stadium became quiet for a profoundly moving memorial ahead of the contest as 10 bells tolled in honor of the city's native Ricky Hatton, who died 46 years old in recently.
It was the premier televised boxing event in the location since the passing of Hatton. As the final chime ended, the stillness transitioned to a roar of "there's just one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the face in the second round, rising shakily to his feet on the count of eight.
But the traditional red attire of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up soon, significant bruising forming under his face as the pair exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over 12 rounds.
The victor barely secured the result with scoring tallies of 114-114, close margin and clearer margin, but both fighters were determined and courageous, exactly what their hero the legend represented.
