British light heavyweight Buatsi earned a win yet disappointing start to his career under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a competitive ten-round fight at the boxing arena.
But the challenger found success, delivering effective single shots in a contest where the techniques didn't complement each other, with excessive holding marring the action.
The scoring judges scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my best performance but what defines champions? They prevail," the victor commented in the arena as he was faced disapproval from the crowd.
The Londoner got back to winning after his maiden career setback - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Several boxing experts believed the challenger, thirty-one, merited the victory but the contender endured the second defeat of his 28-match professional journey.
Buatsi Earns Victory in Dull Match
Buatsi's progress has plateaued in recent years through promotional disputes and extended periods of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He began cautiously, 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 breaking his hand mid-fight, was competing in only his second appearance at the higher weight class.
By the middle rounds, Parker had kept it close, making life awkward for Buatsi, who utilized a solid defense to barely take the more effective stanzas.
The crowd's patience decreased during frequent holding, with the challenger slipping to the canvas various instances during grappling.
Parker ended stronger, but several stanzas were challenging to assess. However, previous titleholder the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, awarding Buatsi just one round.
The victor moves on, but with the likes of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - based on this performance - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the secondary fight, Arthur beat Bradley Rea by split-decision in a terrific all-Manchester battle to secure the European light-heavyweight championship.
The arena became quiet for a extremely emotional homage before the fight as a bell ceremony sounded in remembrance of Manchester's own Ricky Hatton, who died aged 46 in recently.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound ended, the quiet became a shout of "only one Hatton".
The fighting during the bout equaled the emotion. Arthur was sent to the canvas by a left hook flush on the face in the early round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up quickly, noticeable damage appearing under his eye as the duo exchanged punishing blows.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace seldom decreased over twelve rounds.
The victor barely secured the decision with scoring tallies of draw, narrow lead and wider gap, but the two athletes were persistent and brave, exactly what their inspiration the legend embodied.
