UK light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger found success, connecting with powerful single shots in a match where the approaches never quite clicked, with excessive holding marring the contest.
The scoring judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They win," Buatsi commented in the ringside as he was greeted with negative reactions from the spectators.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts believed the challenger, 31, should have been awarded the victory but the contender suffered the second defeat of his 28-bout career.
Buatsi Earns Triumph in Slow Encounter
The fighter's advancement has stalled in the past few years through management issues and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - maybe in what seems like a ultimate opportunity - under new promotional backing.
He started carefully, with neither fighter ready to take risks in a cagey opening few rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in 2022 after damaging his hand during the bout, was making just his second bout at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who operated with a protective stance to barely take the more effective periods.
The spectators' acceptance decreased because of frequent holding, with Parker slipping to the canvas several times during clinches.
Parker closed well, but several stanzas were difficult to score. However, ex-champion Carl Frampton - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol ruling the division, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Tribute Inspires Manchester Derby Battle
In the co-main event, Arthur overcame Rea by split-decision in a terrific all-Manchester fight to capture the European light-heavyweight championship.
The arena grew hushed for a profoundly moving tribute ahead of the contest as a bell ceremony rang in memory of Manchester's own Hatton, who passed away at age 46 in September.
It was the initial significant broadcast fight night in the city since Hatton's death. As the final chime ended, the quiet gave way to a roar of "only one Hatton".
The action during the bout equaled the sentiment. Arthur was floored by a left hook flush on the chin in the early round, rising shakily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon came forward again. Across the ring, the opponent - in competitive blue - was damaged early, noticeable damage appearing under his face as the fighters landed powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the action seldom decreased over twelve rounds.
The victor narrowly won the decision with scoring tallies of draw, 115-113 and wider gap, but the two athletes were relentless and courageous, all the qualities their hero Hatton embodied.
