British light-heavyweight Buatsi earned a win yet unimpressive beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a competitive ten-round bout at the boxing arena.
But the challenger had his moments, delivering effective single shots in a match where the styles didn't complement each other, with constant grabbing marring the contest.
The scoring judges scored it 96-94 to the winner, with the final judge a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi stated in the arena as he was faced disapproval from the spectators.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers felt the challenger, thirty-one, deserved the win but the British boxer experienced the second loss of his 28-match professional journey.
The Champion Earns Victory in Dull Affair
The fighter's advancement has plateaued in the past few years through promotional disputes and extended periods of inactivity.
Earlier forecast as the future of British boxing, he now stands trying to realize his potential - possibly in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers prepared to take risks in a cagey early stages.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for the favorite, who worked behind a solid defense to narrowly win the more effective periods.
The crowd's patience wore thin during frequent holding, with Parker slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but many rounds were difficult to score. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just a single round.
The victor progresses, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Inspires Local Rivalry Battle
In the secondary fight, Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester battle to capture the European light heavyweight championship.
The arena became quiet for a extremely emotional tribute prior to the bout as a bell ceremony rang in memory of the city's native Ricky Hatton, who passed away aged 46 in September.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the concluding sound ended, the stillness became a chant of "there's just one Hatton".
The action within the ring matched the sentiment. Arthur was floored by a left hook directly to the jaw in the early round, rising shakily to his position on the eight count.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up quickly, significant bruising developing under his orbital area as the duo landed powerful shots.
The challenger, 27, landed power punches but Arthur, thirty-four, fought fire with fire with powerful upward punches as the pace rarely dropped over 12 rounds.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and 115-112, but each competitor were relentless and full of heart, everything their idol Hatton represented.
