UK light-heavyweight Buatsi secured a victory yet underwhelming beginning to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a tight ten-round contest at the boxing arena.
But the challenger had his moments, connecting with powerful clean blows in a match where the approaches failed to mesh, with frequent clinching disrupting the action.
The scoring judges had it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my best performance but what do champions do? They prevail," the victor commented in the ringside as he was greeted with boos from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Some ringside observers believed Parker, 31, merited the victory but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Slow Affair
The fighter's advancement has plateaued in the past few years through management issues and long spells of inactivity.
Earlier forecast as the future of UK boxing, he now stands trying to fulfil that early promise - maybe in what feels like a ultimate opportunity - under recent support.
He began cautiously, with the two boxers prepared to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand mid-fight, was competing in only his second fight at light-heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who worked behind a tight guard to edge the better periods.
The crowd's patience decreased during constant clinching, with the challenger slipping to the canvas various instances during close exchanges.
Parker ended stronger, but many rounds were difficult to score. Although, former world champion Carl Frampton - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
The victor moves on, but with the caliber of hard hitter David Benavidez, and Russian star Bivol ruling the division, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Arthur overcame Rea by split-decision in a terrific all-Manchester fight to secure the European light heavyweight title.
The stadium grew hushed for a deeply poignant homage prior to the bout as a bell ceremony sounded in memory of the city's native Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised fight night in the urban center since Hatton's death. As the concluding sound disappeared, the silence became a shout of "there's only one Hatton".
The action within the ring reflected the sentiment. The eventual winner was sent to the canvas by a significant blow squarely on the jaw in the second round, rising shakily to his feet on the count of eight.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was marked up early, heavy swelling forming under his face as the pair traded powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur edged the result with judges scorecards of even score, close margin and wider gap, but each competitor were persistent and courageous, everything their hero the legend embodied.
