UK light heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a judges' verdict in a competitive 10-round fight at the Manchester venue.
But Parker found success, landing some telling clean blows in a contest where the techniques never quite clicked, with frequent clinching marring the action.
The scoring judges scored it 96-94 to the winner, with the third a 95-95.
"It wasn't my best display but what do champions do? They succeed," Buatsi commented in the ring as he was greeted with disapproval from the crowd.
The Londoner bounced back after his first professional defeat - an epic battle with Callum Smith in February - to claim a twentieth professional win.
Various analysts felt the challenger, 31, should have been awarded the victory but the Derbyshire fighter experienced the second setback of his 28-match career.
Buatsi Secures Win in Uneventful Encounter
The fighter's advancement has stalled in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to achieve expectations - possibly in what feels like a last chance - under fresh management.
He began cautiously, with both competitors willing to take risks in a tentative initial rounds.
Parker, whose single earlier setback came at super-middleweight against his former opponent in 2022 after breaking his hand in the contest, was competing in only his second fight at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who operated with a protective stance to narrowly win the better rounds.
The audience's tolerance wore thin because of frequent holding, with Parker falling to the floor various instances during close exchanges.
The underdog ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - working with the broadcast network - had it strongly leaning for Parker, giving Buatsi just one round.
The victor moves on, but with the caliber of hard hitter Benavidez, and Russian star Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Hatton Tribute Inspires Local Rivalry Fight
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a outstanding local rivalry battle to secure the continental title.
The venue grew hushed for a profoundly moving memorial before the fight as 10 bells tolled in memory of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised boxing event in the location since Hatton's passing. As the last bell faded, the quiet transitioned to a shout of "only one Ricky Hatton".
The fighting within the ring reflected the emotion. The eventual winner was sent to the canvas by a significant blow directly to the face in the early round, rising shakily to his position on the referee's count.
But the traditional red equipment of Arthur soon came forward again. From the other corner, Rea - in opposing blue - was marked up early, noticeable damage appearing under his face as the fighters traded punishing blows.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with powerful upward punches as the intensity hardly diminished over twelve rounds.
The victor narrowly won the result with official scores of 114-114, narrow lead and 115-112, but each competitor were determined and courageous, everything their inspiration Hatton represented.
