British light heavyweight Buatsi secured a victory yet disappointing start to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling individual punches in a fight where the techniques didn't complement each other, with excessive holding marring the action.
The officials had it 96-94 to the winner, with the final judge a even score.
"It wasn't my finest performance but how do champions respond? They succeed," the victor commented in the arena as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-bout professional journey.
The Champion Claims Victory in Dull Encounter
Buatsi's progress has plateaued in recent times through management issues and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with both competitors prepared to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was making just his second appearance at light heavyweight.
By the halfway stage, the underdog had kept it close, causing problems for the favorite, who utilized a tight guard to edge the better rounds.
The crowd's patience wore thin because of constant clinching, with Parker slipping to the canvas several times during grappling.
Parker ended stronger, but multiple periods were difficult to score. Although, former world champion Carl Frampton - commentating on the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Fuels Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Rea by close verdict in a outstanding local rivalry battle to capture the European light heavyweight title.
The arena grew hushed for a profoundly moving homage before the fight as 10 bells tolled in remembrance of Manchester's own Hatton, who died aged 46 in last month.
It was the first major televised match card in the location since Hatton's death. As the final chime disappeared, the stillness transitioned to a roar of "there's only one Ricky Hatton".
The action during the bout equaled the emotion. The eventual winner was sent to the canvas by a powerful punch flush on the jaw in the early round, getting up unsteadily to his footing on the count of eight.
But the traditional red shorts of Arthur soon advanced again. On the opposite side, Rea - in competitive blue - was injured early, heavy swelling forming under his orbital area as the pair landed hard punches.
The challenger, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the intensity seldom decreased over the full distance.
The victor barely secured the verdict with official scores of 114-114, close margin and clearer margin, but both fighters were relentless and brave, all the qualities their inspiration Hatton represented.
