UK light-heavyweight Buatsi made a winning yet underwhelming debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a tight ten-round bout at the boxing arena.
But the challenger found success, delivering effective single shots in a match where the techniques failed to mesh, with frequent clinching spoiling the contest.
The officials judged it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest performance but how do champions respond? They win," the victor stated in the arena as he was met by negative reactions from the spectators.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts believed the challenger, 31, merited the decision but the contender experienced the second setback of his 28-fight professional journey.
The Champion Earns Victory in Uneventful Match
Buatsi's progress has plateaued in recent years through contract problems and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now is positioned trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with the two boxers willing to take risks in a tentative early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second appearance at light heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the cleaner periods.
The crowd's patience decreased during constant clinching, with Parker falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were difficult to score. Although, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor progresses, but with the likes of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding local rivalry battle to win the European light heavyweight title.
The venue grew hushed for a extremely emotional tribute before the fight as ten bells tolled in memory of the city's native Hatton, who passed away aged 46 in recently.
It was the premier televised fight night in the urban center since Hatton's passing. As the last bell disappeared, the quiet gave way to a shout of "there's just one Hatton".
The competition inside the ropes matched the sentiment. Arthur was sent to the canvas by a left hook directly to the chin in the early round, rising shakily to his footing on the count of eight.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was marked up soon, noticeable damage appearing under his orbital area as the pair exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, fought fire with fire with effective uppercuts as the intensity rarely dropped over the full distance.
Arthur barely secured the decision with judges scorecards of 114-114, narrow lead and wider gap, but the two athletes were relentless and full of heart, all the qualities their inspiration Hatton stood for.
