UK light heavyweight Joshua Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a tight 10-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the styles didn't complement each other, with constant grabbing marring the action.
Two judges judged it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my best performance but what do champions do? They succeed," the victor said in the arena as he was greeted with disapproval from the crowd.
The Londoner bounced back after his initial pro loss - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, deserved the decision but the Derbyshire fighter suffered the second defeat of his 28-fight professional journey.
Buatsi Claims Win in Slow Match
His career development has slowed in recent years through management issues and long spells of lack of fights.
Previously predicted as the future of British boxing, he now finds himself trying to fulfil that early promise - possibly in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with neither fighter prepared to be aggressive in a cagey opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against his former opponent in two years ago after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who utilized a tight guard to edge the more effective stanzas.
The crowd's patience decreased because of regular grabbing, with Parker falling to the floor multiple occasions during clinches.
Parker closed well, but multiple periods were hard to judge. Although, ex-champion the boxing analyst - providing analysis for Dazn - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor moves on, but with the presence of power puncher Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Tribute Inspires Local Rivalry Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by split-decision in a excellent Manchester vs Manchester fight to win the European light heavyweight championship.
The arena grew hushed for a deeply poignant tribute ahead of the contest as a bell ceremony tolled in honor of Manchester's own Ricky Hatton, who succumbed aged 46 in September.
It was the first major televised fight night in the location since Hatton's passing. As the last bell ended, the quiet gave way to a roar of "there's just one Ricky Hatton".
The competition during the bout matched the emotion. The eventual winner was sent to the canvas by a powerful punch directly to the face in the second round, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up soon, noticeable damage appearing under his face as the duo traded powerful shots.
Rea, 27, delivered effective strikes but the champion, 34, responded in kind with effective uppercuts as the action hardly diminished over twelve rounds.
Arthur barely secured the decision with judges scorecards of even score, close margin and wider gap, but the two athletes were determined and full of heart, everything their hero the legend embodied.
