British light heavyweight Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive ten-round fight at the Manchester venue.
But the challenger found success, connecting with powerful clean blows in a match where the approaches didn't complement each other, with excessive holding spoiling the action.
Two judges judged it 96-94 in favor to Buatsi, with the final judge a 95-95.
"It wasn't my best performance but what do champions do? They prevail," Buatsi said in the arena as he was greeted with disapproval from the crowd.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to secure a 20th pro success.
Several boxing experts felt Parker, 31, merited the victory but the Derbyshire fighter suffered the second loss of his 28-bout career.
Buatsi Claims Victory in Slow Match
His career development has plateaued in the past few years through promotional disputes and considerable time of lack of fights.
Once tipped as the rising talent of British boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers willing to take risks in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a protective stance to narrowly win the better stanzas.
The audience's tolerance decreased amid regular grabbing, with Parker slipping to the canvas multiple occasions during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. Although, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for the challenger, giving Buatsi just a single round.
The victor progresses, but with the caliber of hard hitter David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Hatton Homage Inspires Local Rivalry Fight
In the co-main event, Arthur defeated Rea by close verdict in a terrific local rivalry battle to capture the European light heavyweight title.
The venue grew hushed for a extremely emotional homage prior to the bout as 10 bells sounded in remembrance of the city's native Ricky Hatton, who succumbed aged 46 in September.
It was the premier televised match card in the city since Hatton's death. As the last bell faded, the stillness became a shout of "there's just one Hatton".
The action within the ring matched the emotion. The eventual winner was knocked down by a left hook squarely on the jaw in the second round, rising shakily to his footing on the referee's count.
But the red-colored attire of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was injured early, significant bruising developing under his orbital area as the fighters traded hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with powerful upward punches as the pace hardly diminished over the full distance.
Arthur narrowly won the result with judges scorecards of even score, 115-113 and wider gap, but the two athletes were persistent and brave, all the qualities their idol Hatton embodied.
