UK light heavyweight Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a tight ten-round contest at the Manchester venue.
But Parker had his moments, connecting with powerful single shots in a contest where the styles never quite clicked, with frequent clinching marring the action.
Two judges judged it 96-94 for to Buatsi, with the third a even score.
"It wasn't my greatest showing but what defines champions? They prevail," the victor commented in the arena as he was faced boos from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to earn a 20th pro success.
Some ringside observers thought the challenger, thirty-one, merited the decision but the British boxer experienced the second loss of his 28-fight professional journey.
The Champion Secures Victory in Dull Encounter
Buatsi's progress has stalled in recent times through management issues and considerable time of inactivity.
Previously predicted as the future of UK boxing, he now finds himself trying to realize his potential - maybe in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with the two boxers prepared to take risks in a calculated initial rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second fight at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for the favorite, who operated with a protective stance to narrowly win the more effective stanzas.
The crowd's patience diminished during regular grabbing, with the challenger slipping to the canvas several times during grappling.
The underdog closed well, but many rounds were hard to judge. Nevertheless, former world champion Carl Frampton - 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 hard hitter David Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester contest to secure the European light-heavyweight title.
The stadium became quiet for a profoundly moving homage ahead of the contest as 10 bells tolled in remembrance of the city's native Hatton, who died aged 46 in recently.
It was the initial significant broadcast match card in the urban center since Hatton's passing. As the concluding sound disappeared, the stillness became a chant of "there's just one Ricky Hatton".
The fighting during the bout reflected the sentiment. Arthur was floored by a significant blow directly to the chin in the initial stage, rising shakily to his position on the referee's count.
But the Manchester United-red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in competitive blue - was damaged early, noticeable damage forming under his face as the pair exchanged powerful shots.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur barely secured the result with official scores of 114-114, close margin and clearer margin, but both fighters were determined and brave, everything their idol Hatton represented.
