UK light heavyweight Buatsi secured a victory yet underwhelming beginning to his career under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive ten-round bout at the boxing arena.
But Parker had his moments, connecting with powerful clean blows in a match where the techniques didn't complement each other, with excessive holding spoiling the action.
The scoring judges scored it 96-94 for to Buatsi, with the third a even score.
"It wasn't my finest performance but what defines champions? They succeed," Buatsi commented in the ringside as he was faced negative reactions from the spectators.
The British fighter got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Several boxing experts felt the challenger, 31, should have been awarded the win but the British boxer experienced the second loss of his 28-fight career.
Buatsi Earns Triumph in Uneventful Encounter
The fighter's advancement has slowed in the past few years through management issues and extended periods of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with both competitors willing to take risks in a cagey initial rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a protective stance to edge the better periods.
The crowd's patience diminished during frequent holding, with Parker falling to the floor several times during grappling.
The underdog ended stronger, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
Buatsi moves on, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still appears challenging.
Hatton Tribute Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a outstanding local rivalry battle to win the European light heavyweight belt.
The stadium became quiet for a deeply poignant homage prior to the bout as 10 bells rang in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in recently.
It was the premier televised match card in the urban center since Hatton's passing. As the concluding sound disappeared, the stillness gave way to a chant of "there's just one Hatton".
The competition inside the ropes matched the feeling. Arthur was floored by a significant blow squarely on the jaw in the initial stage, standing uncertainly to his footing on the referee's count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was injured soon, heavy swelling appearing under his eye as the duo traded punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
Arthur narrowly won the decision with scoring tallies of even score, narrow lead and 115-112, but both fighters were determined and brave, everything their idol the legend represented.
