UK light-heavyweight Buatsi secured a victory yet underwhelming debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, delivering effective individual punches in a match where the styles failed to mesh, with constant grabbing spoiling the fight.
Two judges judged it 96-94 for to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest showing but how do champions respond? They succeed," Buatsi said in the arena as he was greeted with boos from the spectators.
The British fighter returned to winning ways after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers thought the challenger, thirty-one, should have been awarded the win but the British boxer suffered the second defeat of his 28-bout career.
The Champion Secures Triumph in Slow Match
His career development has stalled in the past few years through management issues and extended periods of lack of fights.
Previously predicted as the rising talent of British boxing, he now stands trying to fulfil that early promise - possibly in what appears to be a last chance - under new promotional backing.
He began cautiously, with both competitors ready to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second bout at light-heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who operated with a solid defense to barely take the cleaner stanzas.
The spectators' acceptance wore thin amid constant clinching, with Parker going down multiple occasions during clinches.
The underdog finished the stronger, but multiple periods were difficult to score. However, former world champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
Buatsi progresses, but with the likes of power puncher Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still seems difficult.
Hatton Homage Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a terrific local rivalry battle to capture the continental championship.
The stadium became quiet for a deeply poignant memorial prior to the bout as 10 bells rang in memory of the city's native Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the location since the passing of Hatton. As the concluding sound disappeared, the silence became a shout of "there's only one Ricky Hatton".
The competition during the bout matched the emotion. The eventual winner was knocked down by a significant blow directly to the jaw in the initial stage, rising shakily to his position on the referee's count.
But the traditional red shorts of the fighter soon advanced again. Across the ring, the opponent - in opposing blue - was injured quickly, significant bruising appearing under his face as the pair landed hard punches.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the pace hardly diminished over 12 rounds.
The victor narrowly won the result with official scores of draw, 115-113 and 115-112, but the two athletes were relentless and full of heart, all the qualities their idol the legend stood for.
