British light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to his career under new promoters with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a close 10-round contest at the boxing arena.
But Parker found success, landing some telling clean blows in a match where the approaches never quite clicked, with excessive holding disrupting the contest.
The officials had it 96-94 to Buatsi, with the third a 95-95.
"It wasn't my best performance but how do champions respond? They prevail," Buatsi commented in the arena as he was met by boos from the crowd.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers felt Parker, thirty-one, should have been awarded the victory but the contender experienced the second setback of his 28-match professional journey.
The Champion Earns Victory in Uneventful Affair
Buatsi's progress has plateaued in recent years through management issues and considerable time of inactivity.
Once tipped as the future of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what seems like a last chance - under fresh management.
He began cautiously, with both competitors ready to overcommit in a cagey early stages.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after suffering a hand injury in the contest, was participating in his second fight at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to edge the better rounds.
The spectators' acceptance wore thin during frequent holding, with the challenger falling to the floor several times during close exchanges.
Parker ended stronger, but several stanzas were challenging to assess. Although, former world champion the boxing analyst - commentating on Dazn - had it particularly wide for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Hatton Homage Motivates Manchester Derby Fight
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a terrific local rivalry contest to capture the European light heavyweight championship.
The stadium fell silent for a extremely emotional memorial before the fight as a bell ceremony tolled in remembrance of Manchester's own Ricky Hatton, who passed away at age 46 in last month.
It was the premier televised match card in the city since Hatton's death. As the concluding sound faded, the stillness became a shout of "only one Ricky Hatton".
The competition within the ring matched the sentiment. The eventual winner was floored by a powerful punch squarely on the face in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored equipment of Arthur soon advanced again. On the opposite side, the opponent - in opposing blue - was marked up soon, noticeable damage developing under his eye as the pair traded powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace rarely dropped over the full distance.
The victor edged the verdict with judges scorecards of draw, close margin and wider gap, but the two athletes were relentless and full of heart, everything their hero Hatton embodied.
