British light heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a close 10-round fight at the boxing arena.
But Parker had his moments, connecting with powerful single shots in a match where the techniques never quite clicked, with constant grabbing spoiling the fight.
Two judges judged it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my best showing but what do champions do? They prevail," Buatsi said in the arena as he was met by boos from the audience.
The British fighter bounced back after his initial pro loss - an epic battle with Callum Smith in last winter - to earn a twentieth professional win.
Some ringside observers thought the challenger, 31, deserved the victory but the Derbyshire fighter experienced the second setback of his 28-bout career.
The Champion Claims Victory in Dull Match
The fighter's advancement has stalled in recent years through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to achieve expectations - maybe in what appears to be a final roll of the dice - under fresh management.
He started carefully, with neither fighter prepared to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was making just his second bout at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who utilized a solid defense to narrowly win the more effective rounds.
The spectators' acceptance diminished amid regular grabbing, with Parker slipping to the canvas several times during close exchanges.
The underdog finished the stronger, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi moves on, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Memorial Inspires Manchester Derby Fight
In the supporting bout, Lyndon Arthur beat Rea by split-decision in a terrific Manchester vs Manchester contest to secure the continental championship.
The stadium fell silent for a deeply poignant memorial prior to the bout as a bell ceremony tolled in memory of local hero Ricky Hatton, who succumbed 46 years old in September.
It was the premier televised boxing event in the city since Hatton's death. As the concluding sound disappeared, the silence transitioned to a chant of "there's just one Ricky Hatton".
The action during the bout equaled the sentiment. The eventual winner was knocked down by a left hook flush on the jaw in the early round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was damaged early, heavy swelling appearing under his orbital area as the fighters exchanged hard punches.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
The victor edged the decision with judges scorecards of 114-114, close margin and clearer margin, but the two athletes were persistent and courageous, exactly what their hero Hatton represented.
