UK light-heavyweight Buatsi made a winning yet underwhelming start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close ten-round contest at the Manchester venue.
But the challenger had his moments, landing some telling individual punches in a fight where the techniques didn't complement each other, with constant grabbing marring the fight.
The scoring judges scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest showing but what defines champions? They prevail," Buatsi stated in the ring as he was greeted with disapproval from the crowd.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a 20th career victory.
Various analysts thought the challenger, thirty-one, deserved the win but the contender suffered the second defeat of his 28-match professional journey.
Buatsi Claims Victory in Slow Match
Buatsi's progress has stalled in the past few years through management issues and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under new promotional backing.
He opened tentatively, with both competitors prepared to be aggressive in a calculated initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to narrowly win the more effective periods.
The crowd's patience diminished because of constant clinching, with the challenger going down various instances during grappling.
Parker closed well, but multiple periods were challenging to assess. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Tribute Motivates Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding all-Manchester fight to capture the continental title.
The arena became quiet for a extremely emotional tribute prior to the bout as 10 bells tolled in honor of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast boxing event in the urban center since the passing of Hatton. As the last bell ended, the quiet gave way to a roar of "only one Ricky Hatton".
The action during the bout matched the feeling. Arthur was sent to the canvas by a powerful punch flush on the chin in the second round, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, the opponent - in rival City blue - was damaged soon, heavy swelling developing under his face as the duo traded punishing blows.
Rea, twenty-seven, connected with strong blows but Arthur, 34, fought fire with fire with powerful upward punches as the pace rarely dropped over twelve rounds.
Arthur barely secured the decision with judges scorecards of draw, close margin and 115-112, but both fighters were persistent and brave, all the qualities their inspiration the legend represented.
