UK light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a close ten-round contest at the boxing arena.
But Parker had his moments, landing some telling single shots in a contest where the styles failed to mesh, with excessive holding spoiling the fight.
Two judges judged it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi said in the ringside as he was faced boos from the spectators.
The Londoner got back to winning after his initial pro loss - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Some ringside observers thought Parker, 31, should have been awarded the win but the contender endured the second setback of his 28-bout career.
The Champion Secures Victory in Slow Match
The fighter's advancement has stalled in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to achieve expectations - maybe in what feels like a final roll of the dice - under fresh management.
He started carefully, with both competitors ready to take risks in a calculated 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 appearance at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for Buatsi, who utilized a solid defense to barely take the cleaner periods.
The spectators' acceptance diminished because of regular grabbing, with the challenger falling to the floor several times during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. Although, former world champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, awarding Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur beat Rea by divided decision in a terrific local rivalry fight to win the European light heavyweight championship.
The arena fell silent for a deeply poignant homage prior to the bout as a bell ceremony rang in honor of Manchester's own Hatton, who succumbed 46 years old in September.
It was the premier televised match card in the city since Hatton's passing. As the last bell faded, the stillness became a chant of "there's only one Ricky Hatton".
The competition within the ring reflected the feeling. Arthur was sent to the canvas by a powerful punch squarely on the jaw in the second round, rising shakily to his position on the eight count.
But the red-colored attire of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was marked up soon, heavy swelling forming under his eye as the pair exchanged punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, responded in kind with effective uppercuts as the action hardly diminished over the full distance.
The victor narrowly won the result with judges scorecards of even score, 115-113 and wider gap, but the two athletes were relentless and courageous, exactly what their idol the legend stood for.
