UK light-heavyweight Buatsi earned a win yet unimpressive debut to his career under recent management with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a competitive ten-round fight at the boxing arena.
But Parker found success, delivering effective clean blows in a fight where the styles never quite clicked, with frequent clinching marring the contest.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best showing but what do champions do? They win," the victor stated in the arena as he was greeted with boos from the audience.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Various analysts thought the challenger, 31, should have been awarded the win but the British boxer suffered the second defeat of his 28-match career.
The Champion Earns Victory in Uneventful Encounter
The fighter's advancement has stalled in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now stands trying to fulfil that early promise - maybe in what seems like a last chance - under recent support.
He opened tentatively, with the two boxers prepared to be aggressive in a calculated opening few rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who utilized a solid defense to edge the more effective periods.
The crowd's patience diminished because of regular grabbing, with Parker falling to the floor various instances during grappling.
The underdog closed well, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for the challenger, giving Buatsi just one round.
The victor advances, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Fuels Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry fight to win the European light heavyweight belt.
The venue grew hushed for a extremely emotional tribute prior to the bout as a bell ceremony sounded in honor of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the premier televised fight night in the city since Hatton's death. As the concluding sound faded, the quiet transitioned to a chant of "only one Hatton".
The action within the ring equaled the sentiment. The eventual winner was floored by a significant blow directly to the jaw in the second round, standing uncertainly to his feet on the count of eight.
But the red-colored equipment of Arthur soon advanced again. Across the ring, Rea - in competitive blue - was marked up early, noticeable damage appearing under his eye as the duo exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, 34, responded in kind with powerful upward punches as the action rarely dropped over twelve rounds.
Arthur edged the result with official scores of draw, narrow lead and wider gap, but both fighters were determined and courageous, all the qualities their inspiration the legend represented.
