UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a majority decision in a tight ten-round fight at the boxing arena.
But Parker found success, landing some telling clean blows in a match where the styles failed to mesh, with excessive holding disrupting the fight.
The officials had it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest showing but what do champions do? They prevail," Buatsi said in the ringside as he was greeted with boos from the audience.
The Londoner returned to winning ways after his maiden career setback - an thrilling contest with Callum Smith in last winter - to secure a twentieth professional win.
Several boxing experts believed the challenger, 31, deserved the decision but the contender suffered the second defeat of his 28-match career.
Buatsi Claims Win in Slow Match
Buatsi's progress has stalled in recent years through contract problems and extended periods of lack of fights.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - maybe in what appears to be a last chance - under new promotional backing.
He started carefully, with both competitors ready to overcommit in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand during the bout, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had stayed in contention, creating difficulties for the favorite, who worked behind a tight guard to edge the cleaner periods.
The audience's tolerance decreased amid constant clinching, with the challenger falling to the floor several times during grappling.
Parker ended stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the journey to titles - on this evidence - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester fight to capture the European light heavyweight title.
The arena became quiet for a profoundly moving tribute before the fight as ten bells sounded in remembrance of the city's native Ricky Hatton, who died 46 years old in last month.
It was the first major televised match card in the city since the passing of Hatton. As the concluding sound faded, the silence became a roar of "only one Ricky Hatton".
The action within the ring equaled the emotion. Arthur was sent to the canvas by a powerful punch directly to the face in the early round, getting up unsteadily to his position on the eight count.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up soon, significant bruising forming under his eye as the fighters landed punishing blows.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the pace hardly diminished over twelve rounds.
Arthur barely secured the verdict with judges scorecards of draw, close margin and clearer margin, but each competitor were relentless and courageous, everything their hero the legend embodied.
