UK light heavyweight Buatsi made a winning yet underwhelming start to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive ten-round contest at the Manchester venue.
But the challenger had his moments, delivering effective single shots in a contest where the styles failed to mesh, with frequent clinching disrupting the fight.
The officials had it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my best performance but how do champions respond? They succeed," Buatsi said in the arena as he was met by negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Several boxing experts believed the challenger, thirty-one, should have been awarded the win but the British boxer experienced the second defeat of his 28-match professional journey.
Buatsi Earns Win in Dull Encounter
His career development has stalled in recent years through promotional disputes and considerable time of lack of fights.
Once tipped as the next star of the British fight scene, he now is positioned trying to realize his potential - perhaps in what appears to be a final roll of the dice - under recent support.
He began cautiously, 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 2022 after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the better stanzas.
The crowd's patience wore thin amid constant clinching, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just one round.
The victor advances, but with the likes of power puncher David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - based on this performance - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a excellent local rivalry contest to capture the European light heavyweight title.
The arena grew hushed for a extremely emotional homage prior to the bout as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who died 46 years old in September.
It was the initial significant broadcast match card in the urban center since Hatton's death. As the final chime faded, the quiet became a chant of "only one Ricky Hatton".
The action within the ring matched the feeling. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the initial stage, standing uncertainly to his footing on the eight count.
But the traditional red shorts of the fighter soon came forward again. Across the ring, the opponent - in competitive blue - was marked up quickly, heavy swelling developing under his eye as the duo traded hard punches.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the intensity seldom decreased over the full distance.
Arthur narrowly won the decision with scoring tallies of draw, close margin and wider gap, but the two athletes were relentless and brave, everything their hero Hatton represented.
