British light-heavyweight Buatsi secured a victory yet disappointing beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful clean blows in a contest where the styles didn't complement each other, with excessive holding disrupting the action.
The scoring judges had it 96-94 in favor to the winner, with the final judge a 95-95 draw.
"It wasn't my greatest showing but what defines champions? They win," Buatsi commented in the ring as he was greeted with disapproval from the spectators.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts thought the challenger, thirty-one, should have been awarded the decision but the British boxer suffered the second defeat of his 28-bout professional journey.
The Champion Secures Victory in Dull Encounter
Buatsi's progress has slowed in recent years through contract problems and long spells of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with both competitors prepared to be aggressive in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was making just his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, creating difficulties for the favorite, who utilized a solid defense to narrowly win the more effective stanzas.
The spectators' acceptance decreased amid regular grabbing, with the challenger going down various instances during close exchanges.
Parker closed well, but multiple periods were difficult to score. However, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for Parker, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a excellent Manchester vs Manchester fight to win the European light heavyweight championship.
The venue grew hushed for a extremely emotional tribute before the fight as a bell ceremony tolled in memory of the city's native Hatton, who succumbed at age 46 in recently.
It was the premier televised fight night in the location since Hatton's passing. As the last bell ended, the silence became a shout of "only one Ricky Hatton".
The fighting within the ring equaled the emotion. Arthur was knocked down by a powerful punch directly to the jaw in the early round, standing uncertainly to his position on the referee's count.
But the traditional red shorts of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up quickly, significant bruising appearing under his orbital area as the pair traded hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the pace hardly diminished over twelve rounds.
The victor narrowly won the verdict with judges scorecards of even score, narrow lead and 115-112, but both fighters were relentless and courageous, all the qualities their hero the legend stood for.
