British light-heavyweight Buatsi secured a victory yet underwhelming start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a judges' verdict in a tight ten-round contest at the boxing arena.
But Parker found success, connecting with powerful single shots in a contest where the styles failed to mesh, with frequent clinching marring the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They prevail," Buatsi commented in the ring as he was faced boos from the crowd.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in February - to claim a 20th pro success.
Several boxing experts believed the challenger, 31, deserved the decision but the Derbyshire fighter endured the second setback of his 28-fight career.
The Champion Secures Victory in Uneventful Affair
His career development has stalled in the past few years through management issues and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to realize his potential - possibly in what appears to be a last chance - under new promotional backing.
He opened tentatively, with both competitors prepared to overcommit in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the middle rounds, Parker had made it competitive, making life awkward for Buatsi, who utilized a solid defense to edge the better periods.
The audience's tolerance diminished amid constant clinching, with the challenger falling to the floor multiple occasions during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. Although, ex-champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just one round.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Rea by close verdict in a terrific local rivalry contest to secure the European light heavyweight championship.
The arena grew hushed for a profoundly moving memorial before the fight as a bell ceremony sounded in remembrance of the city's native Hatton, who died at age 46 in recently.
It was the first major televised boxing event in the urban center since Hatton's passing. As the concluding sound ended, the stillness gave way to a chant of "only one Hatton".
The competition during the bout reflected the feeling. Arthur was floored by a powerful punch directly to the jaw in the second round, rising shakily to his footing on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was damaged soon, heavy swelling developing under his orbital area as the pair landed hard punches.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over the full distance.
Arthur narrowly won the verdict with official scores of even score, 115-113 and wider gap, but the two athletes were determined and brave, all the qualities their inspiration Hatton represented.
