UK light-heavyweight Joshua Buatsi earned a win yet underwhelming beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight ten-round fight at the boxing arena.
But the challenger found success, delivering effective clean blows in a contest where the techniques failed to mesh, with excessive holding spoiling the action.
The scoring judges judged it 96-94 in favor to Buatsi, with the third a 95-95.
"It wasn't my best showing but what defines champions? They win," the victor said in the ring as he was greeted with disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an epic battle with his previous opponent in February - to secure a 20th career victory.
Various analysts felt the challenger, thirty-one, should have been awarded the decision but the British boxer suffered the second setback of his 28-match career.
The Champion Claims Win in Slow Encounter
Buatsi's progress has stalled in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to realize his potential - possibly in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with neither fighter willing to take risks in a calculated opening few rounds.
The challenger, 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 competing in only his second fight at light heavyweight.
By the fight's midpoint, Parker had made it competitive, making life awkward for the favorite, who utilized a solid defense to barely take the cleaner stanzas.
The crowd's patience diminished amid frequent holding, with the challenger slipping to the canvas various instances during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the presence of hard hitter Benavidez, and Russian champion Bivol leading the category, the path to championship success - judging by this showing - still seems difficult.
Hatton Tribute Motivates Local Rivalry Battle
In the co-main event, Arthur overcame Rea by split-decision in a terrific all-Manchester fight to win the European light-heavyweight belt.
The stadium grew hushed for a deeply poignant memorial ahead of the contest as ten bells tolled in memory of the city's native Hatton, who passed away aged 46 in recently.
It was the premier televised boxing event in the urban center since Hatton's death. As the concluding sound ended, the stillness transitioned to a shout of "there's only one Hatton".
The competition during the bout equaled the emotion. Arthur was floored by a left hook flush on the jaw in the initial stage, standing uncertainly to his footing on the eight count.
But the Manchester United-red shorts of Arthur soon came forward again. On the opposite side, Rea - in rival City blue - was marked up soon, heavy swelling developing under his orbital area as the pair traded punishing blows.
Rea, twenty-seven, delivered effective strikes but the champion, 34, fought fire with fire with powerful upward punches as the intensity hardly diminished over the full distance.
Arthur narrowly won the result with judges scorecards of even score, 115-113 and clearer margin, but both fighters were relentless and courageous, exactly what their inspiration the legend stood for.
