British light-heavyweight Buatsi secured a victory yet underwhelming beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate likely gained him a split decision in a competitive ten-round contest at the boxing arena.
But Parker had his moments, landing some telling clean blows in a match where the techniques failed to mesh, with excessive holding disrupting the fight.
Two judges scored it 96-94 to the winner, with the third a 95-95.
"It wasn't my finest display but what defines champions? They succeed," the victor said in the ringside as he was met by disapproval from the audience.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in February - to earn a twentieth professional win.
Some ringside observers believed Parker, thirty-one, should have been awarded the victory but the Derbyshire fighter experienced the second setback of his 28-fight professional journey.
The Champion Earns Win in Uneventful Encounter
Buatsi's progress has slowed in the past few years through management issues and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He started carefully, with the two boxers ready to be aggressive in a tentative early stages.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was making just his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who operated with a solid defense to edge the cleaner periods.
The spectators' acceptance wore thin because of constant clinching, with the challenger falling to the floor multiple occasions during grappling.
The underdog closed well, but multiple periods were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for the broadcast network - had it strongly leaning for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the presence of power puncher Benavidez, and Russian star Bivol ruling the division, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Motivates Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester fight to win the European light-heavyweight belt.
The venue grew hushed for a deeply poignant homage before the fight as a bell ceremony sounded in honor of Manchester's own Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast fight night in the urban center since the passing of Hatton. As the last bell ended, the stillness transitioned to a roar of "only one Hatton".
The action inside the ropes reflected the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the chin in the second round, getting up unsteadily to his position on the referee's count.
But the red-colored equipment of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was damaged early, noticeable damage appearing under his face as the pair traded hard punches.
Rea, 27, landed power punches but the champion, 34, matched the intensity with stinging uppercuts as the pace rarely dropped over the full distance.
The victor narrowly won the verdict with official scores of even score, narrow lead and wider gap, but each competitor were determined and full of heart, everything their hero the legend stood for.
