UK light heavyweight Joshua Buatsi secured a victory yet disappointing start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a tight ten-round fight at the Co-op Live Arena.
But Parker found success, landing some telling clean blows in a match where the approaches failed to mesh, with constant grabbing marring the action.
The scoring judges scored it 96-94 to the winner, with the third a even score.
"It wasn't my greatest performance but what defines champions? They succeed," the victor said in the ring as he was faced disapproval from the audience.
The Londoner bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to earn a 20th pro success.
Various analysts believed the challenger, thirty-one, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-fight professional journey.
Buatsi Secures Victory in Slow Encounter
His career development has slowed in recent years through contract problems and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now stands trying to achieve expectations - perhaps in what seems like a ultimate opportunity - under fresh management.
He started carefully, with neither fighter prepared to overcommit in a calculated initial rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was making just his second appearance at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, creating difficulties for the favorite, who utilized a solid defense to edge the more effective periods.
The audience's tolerance diminished during regular grabbing, with Parker slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - on this evidence - still appears challenging.
Hatton Tribute Motivates Manchester Derby Contest
In the secondary fight, Arthur overcame Bradley Rea by close verdict in a outstanding Manchester vs Manchester contest to win the continental title.
The venue grew hushed for a profoundly moving tribute prior to the bout as ten bells rang in remembrance of local hero Ricky Hatton, who passed away 46 years old in September.
It was the first major televised match card in the city since the passing of Hatton. As the last bell faded, the silence transitioned to a roar of "only one Ricky Hatton".
The action during the bout matched the sentiment. The eventual winner was sent to the canvas by a left hook directly to the jaw in the initial stage, getting up unsteadily to his position on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured quickly, heavy swelling forming under his orbital area as the fighters traded punishing blows.
Rea, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the pace hardly diminished over 12 rounds.
Arthur narrowly won the result with judges scorecards of even score, 115-113 and wider gap, but each competitor were relentless and full of heart, exactly what their hero Hatton embodied.
