British light heavyweight Buatsi made a winning yet underwhelming beginning to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a majority decision in a competitive ten-round fight at the boxing arena.
But the challenger landed significant shots, delivering effective individual punches in a fight where the techniques failed to mesh, with frequent clinching spoiling the fight.
Two judges judged it 96-94 to the winner, with the remaining official a even score.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi stated in the ringside as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts felt the challenger, thirty-one, should have been awarded the victory but the British boxer endured the second setback of his 28-match professional journey.
The Champion Earns Triumph in Slow Affair
The fighter's advancement has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the next star of British boxing, he now stands trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He began cautiously, with the two boxers willing to overcommit in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the halfway stage, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a tight guard to narrowly win the more effective stanzas.
The audience's tolerance diminished amid frequent holding, with Parker falling to the floor various instances during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light heavyweight championship.
The stadium fell silent for a extremely emotional homage before the fight as a bell ceremony tolled in remembrance of the city's native Hatton, who died aged 46 in September.
It was the initial significant broadcast boxing event in the location since Hatton's death. As the last bell disappeared, the quiet transitioned to a shout of "only one Hatton".
The action inside the ropes matched the sentiment. Arthur was floored by a significant blow directly to the jaw in the initial stage, standing uncertainly to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, the opponent - in rival City blue - was injured early, heavy swelling forming under his eye as the pair traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
Arthur edged the verdict with judges scorecards of draw, narrow lead and 115-112, but both fighters were relentless and courageous, everything their idol Hatton stood for.
