British light heavyweight Buatsi secured a victory yet underwhelming debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close 10-round contest at the Co-op Live Arena.
But Parker had his moments, landing some telling clean blows in a fight where the approaches never quite clicked, with excessive holding spoiling the action.
The officials had it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my finest display but what do champions do? They succeed," Buatsi stated in the arena as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers felt Parker, 31, should have been awarded the victory but the contender experienced the second loss of his 28-fight career.
Buatsi Earns Win in Dull Affair
His career development has plateaued in recent years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - maybe in what feels like a last chance - under recent support.
He opened tentatively, with neither fighter prepared to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who operated with a protective stance to narrowly win the cleaner rounds.
The spectators' acceptance diminished because of constant clinching, with the challenger going down multiple occasions during close exchanges.
The underdog ended stronger, but many rounds were challenging to assess. Nevertheless, ex-champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a excellent local rivalry contest to capture the European light heavyweight championship.
The arena became quiet for a extremely emotional tribute prior to the bout as ten bells rang in honor of Manchester's own Ricky Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the last bell disappeared, the quiet gave way to a roar of "there's only one Hatton".
The action inside the ropes equaled the feeling. Arthur was sent to the canvas by a significant blow squarely on the chin 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. On the opposite side, Rea - in competitive blue - was damaged quickly, significant bruising appearing under his orbital area as the pair traded hard punches.
Rea, 27, connected with strong blows but the champion, 34, responded in kind with effective uppercuts as the pace seldom decreased over the full distance.
Arthur barely secured the result with judges scorecards of even score, close margin and 115-112, but each competitor were determined and full of heart, everything their inspiration the legend stood for.
