UK light-heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a majority decision in a competitive ten-round fight at the boxing arena.
But the challenger found success, connecting with powerful single shots in a match where the styles failed to mesh, with excessive holding spoiling the action.
The officials had it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest performance but what do champions do? They succeed," Buatsi stated in the arena as he was greeted with boos from the crowd.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in last winter - to earn a 20th career victory.
Various analysts felt Parker, thirty-one, deserved the decision but the contender endured the second loss of his 28-match career.
Buatsi Secures Triumph in Dull Affair
The fighter's advancement has slowed in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the next star of the British fight scene, he now finds himself trying to realize his potential - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors prepared to overcommit in a tentative opening few rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in 2022 after damaging his hand in the contest, was participating in his second appearance at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for the favorite, who utilized a tight guard to edge the cleaner stanzas.
The crowd's patience decreased during constant clinching, with Parker slipping to the canvas multiple occasions during clinches.
Parker closed well, but multiple periods were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi progresses, but with the caliber of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Tribute Inspires Manchester Derby Fight
In the secondary fight, Arthur defeated Rea by divided decision in a outstanding all-Manchester contest to secure the continental championship.
The arena fell silent for a deeply poignant tribute ahead of the contest as a bell ceremony sounded in remembrance of local hero Ricky Hatton, who passed away aged 46 in recently.
It was the premier televised boxing event in the city since the passing of Hatton. As the last bell faded, the silence transitioned to a chant of "there's just one Hatton".
The fighting inside the ropes matched the emotion. Arthur was knocked down by a left hook squarely on the face in the early round, getting up unsteadily to his feet on the referee's count.
But the red-colored equipment of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up soon, noticeable damage developing under his orbital area as the duo traded hard punches.
Rea, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with powerful upward punches as the action hardly diminished over 12 rounds.
Arthur barely secured the result with scoring tallies of even score, close margin and 115-112, but each competitor were relentless and courageous, all the qualities their idol the legend represented.
