British light-heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a competitive 10-round fight at the boxing arena.
But the challenger found success, connecting with powerful individual punches in a fight where the techniques failed to mesh, with constant grabbing disrupting the contest.
The scoring judges had it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my finest display but what defines champions? They prevail," Buatsi said in the arena as he was faced disapproval from the audience.
The British fighter returned to winning ways after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, deserved the decision but the British boxer endured the second loss of his 28-match professional journey.
The Champion Secures Triumph in Dull Affair
His career development has slowed in recent years through contract problems and long spells of inactivity.
Once tipped as the rising talent of British boxing, he now finds himself trying to fulfil that early promise - perhaps in what feels like a last chance - under recent support.
He began cautiously, with the two boxers willing to take risks in a calculated opening few rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who worked behind a protective stance to barely take the cleaner stanzas.
The audience's tolerance wore thin because of constant clinching, with the challenger going down various instances during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. However, former world champion the boxing analyst - working with Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Memorial Motivates Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Rea by split-decision in a excellent all-Manchester battle to secure the European light-heavyweight title.
The stadium fell silent for a deeply poignant tribute ahead of the contest as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast match card in the location since Hatton's passing. As the last bell ended, the quiet gave way to a chant of "there's just one Hatton".
The action inside the ropes matched the feeling. The eventual winner was sent to the canvas by a left hook directly to the jaw in the second round, rising shakily to his footing on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured early, noticeable damage forming under his orbital area as the pair traded hard punches.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the intensity rarely dropped over twelve rounds.
The victor narrowly won the decision with official scores of draw, narrow lead and clearer margin, but the two athletes were relentless and brave, exactly what their hero the legend stood for.
