British light heavyweight Buatsi earned a win yet underwhelming debut to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight 10-round contest at the Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a match where the approaches didn't complement each other, with frequent clinching spoiling the fight.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my best display but how do champions respond? They prevail," the victor said in the ring as he was greeted with boos from the audience.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in February - to earn a 20th career victory.
Some ringside observers thought the challenger, thirty-one, should have been awarded the victory but the British boxer endured the second defeat of his 28-bout professional journey.
The Champion Secures Victory in Uneventful Affair
The fighter's advancement has stalled in the past few years through contract problems and extended periods of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers ready to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who utilized a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased during regular grabbing, with Parker falling to the floor several times during grappling.
The underdog ended stronger, but multiple periods were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor moves on, but with the likes of power puncher Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a excellent local rivalry battle to secure the European light-heavyweight title.
The arena fell silent for a profoundly moving homage prior to the bout as 10 bells rang in remembrance of the city's native Hatton, who died 46 years old in September.
It was the premier televised fight night in the location since Hatton's death. As the final chime faded, the silence transitioned to a chant of "there's only one Ricky Hatton".
The action during the bout matched the sentiment. Arthur was sent to the canvas by a left hook directly to the chin in the early round, standing uncertainly to his position on the eight count.
But the red-colored equipment of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was marked up early, noticeable damage developing under his eye as the pair exchanged powerful shots.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
Arthur narrowly won the result with scoring tallies of draw, 115-113 and 115-112, but both fighters were relentless and courageous, everything their idol the legend represented.
