UK light heavyweight Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a split decision in a close ten-round bout at the boxing arena.
But the challenger found success, landing some telling single shots in a match where the approaches didn't complement each other, with excessive holding marring the action.
The scoring judges scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," the victor said in the ringside as he was faced boos from the audience.
The Londoner got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts thought the challenger, 31, deserved the decision but the contender experienced the second loss of his 28-fight professional journey.
The Champion Earns Triumph in Slow Match
Buatsi's progress has stalled in the past few years through management issues and long spells of lack of fights.
Earlier forecast as the future of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers prepared to be aggressive in a calculated early stages.
The challenger, whose single earlier setback came at the lower weight class against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at light heavyweight.
By the halfway stage, Parker had kept it close, making life awkward for Buatsi, who operated with a protective stance to barely take the more effective stanzas.
The spectators' acceptance decreased because of frequent holding, with Parker falling to the floor various instances during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. Although, former world champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - on this evidence - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Battle
In the secondary fight, Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester contest to secure the European light-heavyweight title.
The arena grew hushed for a deeply poignant memorial prior to the bout as a bell ceremony tolled in memory of the city's native Hatton, who succumbed 46 years old in September.
It was the premier televised boxing event in the city since Hatton's passing. As the concluding sound ended, the quiet gave way to a shout of "only one Ricky Hatton".
The competition during the bout equaled the emotion. The eventual winner was knocked down by a significant blow squarely on the chin in the early round, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of the fighter soon came forward again. From the other corner, the opponent - in opposing blue - was damaged quickly, noticeable damage forming under his face as the fighters traded powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor barely secured the result with scoring tallies of 114-114, narrow lead and clearer margin, but each competitor were determined and full of heart, everything their idol the legend embodied.
