British light-heavyweight Buatsi made a winning yet underwhelming beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a split decision in a competitive 10-round contest at the boxing arena.
But the challenger landed significant shots, landing some telling single shots in a fight where the styles never quite clicked, with excessive holding spoiling the fight.
Two judges judged it 96-94 for to the winner, with the final judge a even score.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi stated in the ring as he was met by boos from the crowd.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Various analysts thought Parker, 31, merited the decision but the Derbyshire fighter suffered the second loss of his 28-fight career.
Buatsi Earns Victory in Uneventful Affair
Buatsi's progress has slowed in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what seems like a final roll of the dice - under recent support.
He started carefully, with both competitors willing to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second appearance at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to barely take the cleaner stanzas.
The audience's tolerance diminished amid constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but many rounds were difficult to score. However, previous titleholder the boxing analyst - commentating on Dazn - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Hatton Memorial Motivates Local Rivalry Fight
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a terrific local rivalry fight to win the European light-heavyweight title.
The arena became quiet for a extremely emotional homage prior to the bout as 10 bells rang in honor of local hero Ricky Hatton, who succumbed 46 years old in last month.
It was the first major televised match card in the city since Hatton's death. As the concluding sound disappeared, the quiet gave way to a roar of "there's just one Ricky Hatton".
The fighting within the ring reflected the feeling. The eventual winner was floored by a powerful punch directly to the chin in the second round, rising shakily to his footing on the eight count.
But the Manchester United-red attire of the fighter soon pressed ahead again. Across the ring, the opponent - in rival City blue - was damaged soon, heavy swelling developing under his face as the duo exchanged punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the action hardly diminished over 12 rounds.
The victor narrowly won the decision with judges scorecards of draw, 115-113 and 115-112, but both fighters were relentless and courageous, exactly what their hero the legend represented.
