British light-heavyweight Buatsi secured a victory 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 judges' verdict in a competitive ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful single shots in a match where the techniques didn't complement each other, with excessive holding marring the fight.
The scoring judges scored it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi commented in the ringside as he was met by boos from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts thought the challenger, 31, deserved the victory but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Secures Victory in Slow Encounter
Buatsi's progress has plateaued in recent years through contract problems and long spells of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a cagey early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after damaging his hand mid-fight, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who utilized a solid defense to edge the cleaner periods.
The crowd's patience wore thin amid regular grabbing, with Parker slipping to the canvas multiple occasions during clinches.
The underdog closed well, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, giving Buatsi just one round.
Buatsi moves on, but with the likes of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Fuels Local Rivalry Battle
In the supporting bout, Arthur overcame Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to capture the continental belt.
The stadium fell silent for a deeply poignant homage prior to the bout as a bell ceremony sounded in memory of the city's native Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the last bell disappeared, the silence gave way to a shout of "only one Hatton".
The action inside the ropes matched the feeling. The eventual winner was knocked down by a significant blow flush on the face in the initial stage, getting up unsteadily to his feet on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. From the other corner, Rea - in competitive blue - was damaged soon, heavy swelling appearing under his face as the fighters traded hard punches.
Rea, 27, delivered effective strikes but the champion, 34, fought fire with fire with effective uppercuts as the pace seldom decreased over the full distance.
The victor barely secured the verdict with scoring tallies of draw, 115-113 and 115-112, but each competitor were relentless and full of heart, everything their hero the legend represented.
