British light-heavyweight Buatsi earned a win yet disappointing start to life under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a split decision in a competitive 10-round contest at the Manchester venue.
But the challenger found success, delivering effective individual punches in a contest where the styles never quite clicked, with excessive holding disrupting the contest.
The officials had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but what do champions do? They prevail," the victor commented in the arena as he was greeted with disapproval from the spectators.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Several boxing experts thought the challenger, 31, deserved the decision but the contender experienced the second setback of his 28-bout career.
Buatsi Claims Win in Dull Affair
Buatsi's progress has slowed in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to achieve expectations - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter ready to overcommit in a cagey opening few rounds.
Parker, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second bout at light heavyweight.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who operated with a tight guard to edge the better rounds.
The audience's tolerance decreased amid frequent holding, with Parker going down several times during clinches.
Parker ended stronger, but many rounds were hard to judge. However, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Fuels Manchester Derby Battle
In the supporting bout, Arthur defeated Rea by divided decision in a outstanding all-Manchester contest to secure the continental title.
The venue became quiet for a profoundly moving tribute prior to the bout as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the first major televised match card in the location since Hatton's death. As the last bell faded, the silence transitioned to a shout of "only one Hatton".
The fighting during the bout reflected the sentiment. Arthur was knocked down by a significant blow squarely on the face in the initial stage, standing uncertainly to his feet on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, the opponent - in opposing blue - was marked up early, significant bruising developing under his orbital area as the pair landed hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor narrowly won the result with official scores of even score, 115-113 and wider gap, but each competitor were relentless and courageous, exactly what their hero the legend embodied.
