UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a close 10-round contest at the Co-op Live Arena.
But Parker had his moments, delivering effective single shots in a contest where the approaches failed to mesh, with excessive holding marring the action.
The scoring judges judged it 96-94 to the winner, with the third a even score.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi stated in the ring as he was faced disapproval from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers believed Parker, 31, should have been awarded the victory but the British boxer suffered the second defeat of his 28-fight career.
The Champion Secures Win in Dull Encounter
The fighter's advancement has stalled in recent times through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a final roll of the dice - under recent support.
He started carefully, with neither fighter willing to overcommit in a calculated initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had stayed in contention, making life awkward for Buatsi, who operated with a protective stance to narrowly win the better periods.
The crowd's patience diminished during frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. Although, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Memorial Inspires Manchester Derby Contest
In the co-main event, Arthur overcame Bradley Rea by split-decision in a outstanding Manchester vs Manchester contest to capture the European light-heavyweight championship.
The arena became quiet for a deeply poignant homage prior to the bout as a bell ceremony tolled in memory of Manchester's own Hatton, who passed away 46 years old in September.
It was the premier televised match card in the urban center since Hatton's passing. As the final chime faded, the stillness transitioned to a shout of "only one Ricky Hatton".
The competition inside the ropes matched the sentiment. The eventual winner was knocked down by a powerful punch flush on the chin in the early round, getting up unsteadily to his footing on the eight count.
But the Manchester United-red equipment of Arthur soon came forward again. From the other corner, Rea - in competitive blue - was injured early, significant bruising developing under his eye as the fighters landed hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, responded in kind with stinging uppercuts as the intensity seldom decreased over the full distance.
The victor edged the result with official scores of even score, 115-113 and wider gap, but both fighters were determined and brave, exactly what their idol Hatton represented.
