British light heavyweight Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close 10-round contest at the Manchester venue.
But Parker had his moments, landing some telling single shots in a contest where the approaches failed to mesh, with frequent clinching marring the contest.
The scoring judges had it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest display but what defines champions? They succeed," the victor stated in the ring as he was greeted with negative reactions from the spectators.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts thought the challenger, thirty-one, should have been awarded the win but the contender experienced the second defeat of his 28-bout professional journey.
Buatsi Earns Win in Uneventful Affair
The fighter's advancement has slowed in recent years through contract problems and considerable time of lack of fights.
Earlier forecast as the next star of British boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to be aggressive in a cagey initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second bout at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a solid defense to edge the cleaner stanzas.
The audience's tolerance diminished amid constant clinching, with the challenger going down multiple occasions during clinches.
The underdog ended stronger, but many rounds were difficult to score. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the likes of power puncher David Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Hatton Tribute Fuels Manchester Derby Fight
In the co-main event, Arthur overcame Rea by split-decision in a excellent all-Manchester contest to secure the European light heavyweight title.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as ten bells rang in honor of Manchester's own Hatton, who died aged 46 in September.
It was the premier televised match card in the city since Hatton's passing. As the final chime faded, the stillness gave way to a shout of "there's just one Hatton".
The competition inside the ropes reflected the emotion. The eventual winner was floored by a left hook directly to the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up early, noticeable damage developing under his orbital area as the pair exchanged punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action rarely dropped over twelve rounds.
Arthur narrowly won the decision with official scores of even score, 115-113 and clearer margin, but each competitor were persistent and brave, exactly what their inspiration the legend stood for.
