UK light heavyweight Buatsi made a winning yet underwhelming beginning to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a tight 10-round bout at the boxing arena.
But Parker landed significant shots, delivering effective individual punches in a fight where the techniques failed to mesh, with constant grabbing marring the action.
The officials had it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best display but how do champions respond? They prevail," Buatsi said in the arena as he was greeted with negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an memorable fight with Callum Smith in February - to claim a 20th pro success.
Several boxing experts felt Parker, thirty-one, merited the win but the contender experienced the second loss of his 28-bout professional journey.
Buatsi Secures Victory in Slow Match
The fighter's advancement has stalled in recent years through management issues and extended periods of lack of fights.
Previously predicted as the next star of British boxing, he now stands trying to realize his potential - possibly in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors willing to take risks in a tentative early stages.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was competing in only his second fight at the higher weight class.
By the middle rounds, the underdog had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The spectators' acceptance wore thin during constant clinching, with the challenger going down multiple occasions during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. However, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Memorial Fuels Manchester Derby Fight
In the supporting bout, Arthur overcame Rea by split-decision in a terrific all-Manchester battle to secure the European light heavyweight title.
The stadium grew hushed for a extremely emotional tribute before the fight as 10 bells sounded in remembrance of Manchester's own Hatton, who succumbed aged 46 in recently.
It was the first major televised fight night in the location since Hatton's passing. As the last bell disappeared, the stillness became a shout of "only one Ricky Hatton".
The fighting within the ring reflected the emotion. Arthur was sent to the canvas by a powerful punch flush on the chin in the second round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red attire of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged soon, heavy swelling appearing under his orbital area as the duo exchanged powerful shots.
The challenger, twenty-seven, delivered effective strikes but Arthur, 34, fought fire with fire with powerful upward punches as the intensity hardly diminished over the full distance.
The victor narrowly won the decision with scoring tallies of even score, close margin and 115-112, but the two athletes were persistent and brave, everything their hero Hatton stood for.
