UK light heavyweight Buatsi earned a win yet unimpressive debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close ten-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling individual punches in a contest where the styles never quite clicked, with frequent clinching marring the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my finest showing but what defines champions? They win," the victor commented in the arena as he was greeted with negative reactions from the audience.
The Londoner bounced back after his maiden career setback - an epic battle with Callum Smith in February - to secure a 20th career victory.
Several boxing experts believed Parker, thirty-one, should have been awarded the decision but the contender suffered the second defeat of his 28-bout career.
The Champion Claims Victory in Dull Encounter
Buatsi's progress has stalled in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - perhaps in what feels like a last chance - under new promotional backing.
He began cautiously, with neither fighter willing to be aggressive in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was making just his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who operated with a tight guard to narrowly win the better rounds.
The spectators' acceptance wore thin amid constant clinching, with the challenger going down various instances during clinches.
The underdog ended stronger, but several stanzas were difficult to score. Although, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Inspires Local Rivalry Contest
In the supporting bout, Arthur beat Rea by close verdict in a excellent Manchester vs Manchester contest to win the European light heavyweight belt.
The stadium 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 passed away aged 46 in September.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the final chime ended, the silence gave way to a shout of "there's just one Hatton".
The competition inside the ropes matched the sentiment. Arthur was knocked down by a significant blow directly to the chin in the initial stage, rising shakily to his position on the referee's count.
But the traditional red equipment of the fighter soon came forward again. Across the ring, Rea - in competitive blue - was marked up quickly, heavy swelling developing under his orbital area as the duo exchanged punishing blows.
Rea, twenty-seven, landed power punches but Arthur, thirty-four, fought fire with fire with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur barely secured the verdict with official scores of draw, close margin and 115-112, but the two athletes were persistent and brave, everything their hero the legend embodied.
