British light heavyweight Joshua Buatsi earned a win yet disappointing debut to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a tight ten-round contest at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a fight where the techniques never quite clicked, with frequent clinching marring the fight.
Two judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They prevail," Buatsi stated in the arena as he was greeted with boos from the crowd.
The British fighter got back to winning after his maiden career setback - an thrilling contest with Callum Smith in last winter - to claim a twentieth professional win.
Some ringside observers thought Parker, thirty-one, deserved the decision but the British boxer endured the second loss of his 28-match career.
Buatsi Earns Triumph in Uneventful Match
His career development has stalled in recent times through contract problems and long spells of inactivity.
Previously predicted as the rising talent of British boxing, he now is positioned trying to realize his potential - maybe in what feels like a final roll of the dice - under recent support.
He began cautiously, with neither fighter ready to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, making life awkward for the favorite, who worked behind a solid defense to narrowly win the more effective stanzas.
The audience's tolerance wore thin because of constant clinching, with the challenger slipping to the canvas multiple occasions during grappling.
Parker finished the stronger, but many rounds were hard to judge. Nevertheless, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Russian star Bivol leading the category, the journey to titles - based on this performance - still looks steep.
Hatton Memorial Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur defeated Bradley Rea by close verdict in a terrific local rivalry fight to secure the European light heavyweight championship.
The venue fell silent for a profoundly moving tribute before the fight as a bell ceremony rang in honor of the city's native Hatton, who died 46 years old in last month.
It was the premier televised boxing event in the urban center since Hatton's death. As the final chime ended, the stillness became a shout of "there's only one Hatton".
The competition during the bout matched the emotion. The eventual winner was knocked down by a left hook flush on the face in the initial stage, getting up unsteadily to his footing on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was marked up soon, significant bruising appearing under his orbital area as the fighters exchanged hard punches.
The challenger, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with effective uppercuts as the action hardly diminished over the full distance.
The victor narrowly won the verdict with official scores of even score, narrow lead and wider gap, but both fighters were relentless and brave, all the qualities their inspiration the legend represented.
