British light-heavyweight Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive ten-round fight at the Manchester venue.
But Parker had his moments, landing some telling single shots in a fight where the approaches didn't complement each other, with excessive holding spoiling the action.
The officials had it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my greatest display but what defines champions? They succeed," Buatsi stated in the ring as he was faced disapproval from the spectators.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to claim a twentieth professional win.
Several boxing experts thought Parker, 31, merited the win but the contender endured the second loss of his 28-bout career.
The Champion Earns Victory in Dull Affair
His career development has stalled in recent times through contract problems and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now finds himself trying to realize his potential - possibly in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers ready to overcommit in a calculated opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after breaking his hand during the bout, was competing in only his second bout at light-heavyweight.
By the middle rounds, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a protective stance to edge the more effective periods.
The spectators' acceptance decreased amid frequent holding, with the challenger slipping to the canvas multiple occasions during grappling.
Parker ended stronger, but many rounds were challenging to assess. However, former world champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, giving Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the secondary fight, Arthur overcame Rea by split-decision in a outstanding all-Manchester battle to win the European light-heavyweight belt.
The arena grew hushed for a extremely emotional tribute prior to the bout as a bell ceremony rang in honor of the city's native Hatton, who passed away 46 years old in recently.
It was the first major televised boxing event in the city since Hatton's passing. As the concluding sound faded, the quiet transitioned to a chant of "only one Ricky Hatton".
The action inside the ropes matched the sentiment. The eventual winner was knocked down by a left hook directly to the chin in the second round, getting up unsteadily to his position on the eight count.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was damaged early, significant bruising forming under his eye as the fighters traded punishing blows.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur narrowly won the decision with scoring tallies of draw, narrow lead and 115-112, but the two athletes were persistent and courageous, exactly what their inspiration Hatton stood for.
