UK light heavyweight Buatsi secured a victory yet disappointing debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a close 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a contest where the approaches never quite clicked, with frequent clinching marring the fight.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best display but what do champions do? They succeed," Buatsi stated in the ring as he was met by negative reactions from the crowd.
The British fighter bounced back after his initial pro loss - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Various analysts thought Parker, thirty-one, deserved the decision but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Secures Triumph in Slow Encounter
The fighter's advancement has slowed in recent times through promotional disputes and long spells of inactivity.
Once tipped as the future of British boxing, he now stands trying to realize his potential - perhaps in what seems like a final roll of the dice - under new promotional backing.
He opened tentatively, with the two boxers prepared to be aggressive in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to barely take the more effective periods.
The crowd's patience wore thin amid frequent holding, with Parker falling to the floor multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Nevertheless, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the presence of power puncher David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Homage Fuels All-Manchester Battle
In the supporting bout, Arthur overcame Bradley Rea by close verdict in a excellent Manchester vs Manchester fight to win the European light heavyweight belt.
The stadium became quiet for a deeply poignant tribute prior to the bout as a bell ceremony tolled in remembrance of local hero Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the urban center since Hatton's death. As the final chime ended, the quiet transitioned to a shout of "only one Hatton".
The action inside the ropes reflected the emotion. The eventual winner was floored by a left hook flush on the jaw in the second round, getting up unsteadily to his position on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, the opponent - in opposing blue - was injured quickly, heavy swelling developing under his orbital area as the fighters exchanged powerful shots.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the action hardly diminished over 12 rounds.
The victor barely secured the verdict with scoring tallies of even score, narrow lead and wider gap, but each competitor were determined and full of heart, everything their hero the legend embodied.
