UK light heavyweight Buatsi earned a win yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a tight ten-round bout at the Manchester venue.
But Parker found success, connecting with powerful clean blows in a fight where the styles failed to mesh, with excessive holding disrupting the fight.
The scoring judges had it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi said in the arena as he was met by boos from the crowd.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in last winter - to earn a 20th career victory.
Several boxing experts believed the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second loss of his 28-match professional journey.
The Champion Claims Triumph in Dull Affair
Buatsi's progress has slowed in recent years through promotional disputes and extended periods of lack of fights.
Once tipped as the future of British boxing, he now is positioned trying to realize his potential - possibly in what seems like a ultimate opportunity - under fresh management.
He opened tentatively, with neither fighter prepared to be aggressive in a cagey initial rounds.
The challenger, 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 competing in only his second fight at the higher weight class.
By the fight's midpoint, Parker had made it competitive, causing problems for Buatsi, who operated with a protective stance to edge the more effective stanzas.
The spectators' acceptance diminished amid constant clinching, with the challenger slipping to the canvas several times during close exchanges.
The underdog closed well, but several stanzas were challenging to assess. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the road to world glory - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a terrific all-Manchester fight to capture the European light-heavyweight belt.
The arena became quiet for a deeply poignant homage before the fight as a bell ceremony rang in honor of Manchester's own Ricky Hatton, who passed away aged 46 in September.
It was the first major televised match card in the city since Hatton's death. As the last bell ended, the quiet transitioned to a shout of "there's just one Hatton".
The action inside the ropes reflected the sentiment. The eventual winner was sent to the canvas by a significant blow flush on the chin in the initial stage, getting up unsteadily to his footing on the count of eight.
But the traditional red attire of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was marked up soon, noticeable damage appearing under his orbital area as the duo exchanged hard punches.
Rea, twenty-seven, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the result with judges scorecards of even score, close margin and wider gap, but the two athletes were persistent and full of heart, exactly what their inspiration the legend embodied.
