UK light-heavyweight Buatsi made a winning yet unimpressive debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a tight ten-round fight at the boxing arena.
But Parker landed significant shots, connecting with powerful individual punches in a match where the approaches failed to mesh, with excessive holding disrupting the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but what do champions do? They prevail," the victor commented in the ring as he was met by boos from the spectators.
The British fighter got back to winning after his initial pro loss - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Various analysts thought the challenger, 31, deserved the victory but the Derbyshire fighter endured the second setback of his 28-match professional journey.
The Champion Secures Triumph in Slow Affair
His career development has stalled in the past few years through promotional disputes and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with the two boxers willing to take risks in a cagey opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second fight at light heavyweight.
By the middle rounds, Parker had kept it close, causing problems for the favorite, who operated with a tight guard to narrowly win the better periods.
The audience's tolerance wore thin during frequent holding, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. However, former world champion Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, awarding Buatsi just one round.
Buatsi advances, but with the caliber of heavy hitter David Benavidez, and Russian champion Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Fuels All-Manchester Fight
In the secondary fight, Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester contest to secure the European light-heavyweight title.
The venue grew hushed for a deeply poignant memorial before the fight as a bell ceremony tolled in memory of the city's native Ricky Hatton, who died 46 years old in recently.
It was the initial significant broadcast fight night in the location since Hatton's death. As the concluding sound disappeared, the stillness gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout reflected the feeling. Arthur was sent to the canvas by a powerful punch squarely on the jaw in the second round, standing uncertainly to his footing on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was injured soon, significant bruising forming under his orbital area as the duo exchanged powerful shots.
The challenger, 27, connected with strong blows but Arthur, thirty-four, responded in kind with stinging uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the verdict with official scores of even score, 115-113 and 115-112, but the two athletes were persistent and brave, everything their hero Hatton stood for.
