UK light heavyweight Buatsi secured a victory yet disappointing start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight ten-round bout at the boxing arena.
But the challenger had his moments, landing some telling clean blows in a fight where the approaches didn't complement each other, with excessive holding spoiling the fight.
The officials scored it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my finest display but what do champions do? They succeed," Buatsi said in the ring as he was greeted with boos from the crowd.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought Parker, thirty-one, should have been awarded the win but the contender experienced the second setback of his 28-fight professional journey.
The Champion Secures Victory in Uneventful Affair
His career development has plateaued in recent times through contract problems and extended periods of lack of fights.
Once tipped as the future of UK boxing, he now is positioned trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under recent support.
He started carefully, with the two boxers willing to overcommit in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in 2022 after suffering a hand injury during the bout, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the cleaner rounds.
The audience's tolerance wore thin amid regular grabbing, with the challenger going down multiple occasions during grappling.
The underdog ended stronger, but many rounds were hard to judge. However, ex-champion the boxing analyst - commentating on Dazn - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of heavy hitter David Benavidez, and Russian star Bivol ruling the division, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a excellent all-Manchester contest to capture the European light heavyweight belt.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as ten bells tolled in honor of local hero Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised boxing event in the location since Hatton's death. As the final chime faded, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The competition within the ring reflected the sentiment. The eventual winner was knocked down by a significant blow squarely on the chin in the early round, rising shakily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was injured early, noticeable damage forming under his eye as the duo traded punishing blows.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with effective uppercuts as the action rarely dropped over the full distance.
The victor narrowly won the decision with scoring tallies of draw, narrow lead and 115-112, but the two athletes were determined and courageous, exactly what their idol the legend embodied.
