British light heavyweight Buatsi made a winning yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a tight ten-round bout at the boxing arena.
But the challenger had his moments, landing some telling single shots in a contest where the techniques never quite clicked, with frequent clinching marring the contest.
Two judges scored it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my greatest performance but what defines champions? They succeed," the victor commented in the ringside as he was met by negative reactions from the audience.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in last winter - to claim a 20th career victory.
Several boxing experts thought Parker, 31, merited the win but the British boxer experienced the second setback of his 28-match career.
Buatsi Claims Victory in Dull Encounter
His career development has stalled in the past few years through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of UK boxing, he now stands trying to realize his potential - perhaps in what seems like a last chance - under recent support.
He started carefully, with neither fighter willing to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in two years ago after breaking his hand in the contest, was participating in his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, creating difficulties for Buatsi, who utilized a protective stance to edge the more effective stanzas.
The audience's tolerance decreased amid constant clinching, with Parker slipping to the canvas multiple occasions during grappling.
Parker closed well, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Memorial Motivates All-Manchester Fight
In the co-main event, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent Manchester vs Manchester contest to capture the continental title.
The venue fell silent for a extremely emotional tribute before the fight as 10 bells sounded in remembrance of local hero Hatton, who died aged 46 in recently.
It was the first major televised match card in the location since the passing of Hatton. As the last bell disappeared, the stillness transitioned to a shout of "only one Ricky Hatton".
The competition within the ring reflected the feeling. The eventual winner was sent to the canvas by a significant blow flush on the jaw in the second round, standing uncertainly to his footing on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. Across the ring, the opponent - in competitive blue - was injured soon, significant bruising developing under his face as the fighters landed powerful shots.
The challenger, 27, landed power punches but the champion, 34, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
The victor edged the verdict with scoring tallies of 114-114, 115-113 and 115-112, but the two athletes were determined and brave, all the qualities their inspiration the legend embodied.
