UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a judges' verdict in a tight 10-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective individual punches in a contest where the techniques failed to mesh, with excessive holding marring the contest.
The scoring judges scored it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best display but what do champions do? They prevail," the victor said in the ring as he was greeted with disapproval from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with his previous opponent in last winter - to secure a 20th pro success.
Various analysts believed Parker, thirty-one, should have been awarded the victory but the British boxer suffered the second defeat of his 28-bout professional journey.
The Champion Secures Triumph in Dull Affair
The fighter's advancement has plateaued in recent years through contract problems and considerable time of lack of fights.
Previously predicted as the future of UK boxing, he now finds himself trying to achieve expectations - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers ready to take risks in a calculated opening few rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who operated with a protective stance to edge the cleaner stanzas.
The spectators' acceptance wore thin during constant clinching, with Parker falling to the floor several times during grappling.
Parker ended stronger, but several stanzas were hard to judge. Although, former world champion the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, awarding Buatsi just only one stanza.
Buatsi moves on, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Motivates Local Rivalry Contest
In the co-main event, Arthur defeated Rea by divided decision in a excellent local rivalry contest to secure the European light-heavyweight belt.
The stadium grew hushed for a extremely emotional memorial prior to the bout as a bell ceremony tolled in memory of Manchester's own Ricky Hatton, who died 46 years old 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 roar of "there's just one Ricky Hatton".
The fighting during the bout equaled the feeling. The eventual winner was floored by a powerful punch flush on the face in the early round, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was marked up early, noticeable damage appearing under his orbital area as the duo exchanged punishing blows.
The challenger, twenty-seven, landed power punches but Arthur, thirty-four, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
The victor edged the result with official scores of even score, close margin and clearer margin, but the two athletes were relentless and courageous, exactly what their hero the legend embodied.
