UK light heavyweight Buatsi secured a victory yet underwhelming beginning to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a close ten-round fight at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a contest where the techniques failed to mesh, with frequent clinching marring the contest.
The officials scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best showing but what do champions do? They win," Buatsi said in the ring as he was met by negative reactions from the spectators.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Several boxing experts believed the challenger, thirty-one, deserved the decision but the Derbyshire fighter experienced the second setback of his 28-bout professional journey.
The Champion Claims Triumph in Slow Match
Buatsi's progress has slowed in recent years through management issues and extended periods of inactivity.
Once tipped as the rising talent of British boxing, he now is positioned trying to realize his potential - maybe in what appears to be a final roll of the dice - under recent support.
He started carefully, with the two boxers willing to overcommit in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after suffering a hand injury in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for Buatsi, who operated with a solid defense to edge the more effective stanzas.
The spectators' acceptance wore thin because of frequent holding, with the challenger slipping to the canvas various instances during close exchanges.
The underdog finished the stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for the challenger, giving Buatsi just one round.
Buatsi progresses, but with the presence of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the path to championship success - judging by this showing - still appears challenging.
Ricky Hatton Homage Inspires All-Manchester Fight
In the secondary fight, Arthur defeated Bradley Rea by split-decision in a terrific Manchester vs Manchester fight to secure the European light heavyweight belt.
The venue fell silent for a deeply poignant homage before the fight as 10 bells rang in remembrance of local hero Ricky Hatton, who succumbed at age 46 in last month.
It was the premier televised boxing event in the city since the passing of Hatton. As the last bell faded, the quiet became a roar of "only one Hatton".
The fighting inside the ropes matched the sentiment. The eventual winner was sent to the canvas by a significant blow squarely on the chin in the early round, rising shakily to his footing on the eight count.
But the Manchester United-red equipment of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was damaged early, heavy swelling developing under his eye as the duo landed hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the action rarely dropped over twelve rounds.
Arthur barely secured the verdict with judges scorecards of even score, close margin and 115-112, but the two athletes were persistent and brave, everything their inspiration the legend represented.
