British light heavyweight Joshua Buatsi earned a win yet underwhelming beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round bout at the boxing arena.
But the challenger landed significant shots, landing some telling clean blows in a contest where the styles failed to mesh, with constant grabbing disrupting the fight.
The scoring judges scored it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my finest performance but how do champions respond? They succeed," the victor said in the ringside as he was greeted with negative reactions from the spectators.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Several boxing experts thought Parker, thirty-one, should have been awarded the win but the British boxer experienced the second loss of his 28-match career.
The Champion Claims Triumph in Dull Affair
The fighter's advancement has slowed in recent years through management issues and long spells of lack of fights.
Earlier forecast as the next star of British boxing, he now stands trying to fulfil that early promise - maybe in what seems like a final roll of the dice - under fresh management.
He started carefully, with both competitors prepared to overcommit in a tentative opening few rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in two years ago after breaking his hand in the contest, was competing in only his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The audience's tolerance wore thin because of frequent holding, with Parker slipping to the canvas multiple occasions during clinches.
The underdog closed well, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - commentating on Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
The victor advances, but with the caliber of heavy hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - judging by this showing - still looks steep.
Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a outstanding Manchester vs Manchester fight to win the European light heavyweight belt.
The venue fell silent for a profoundly moving memorial before the fight as a bell ceremony tolled in memory of the city's native Ricky Hatton, who passed away aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's death. As the last bell disappeared, the quiet gave way to a chant of "there's just one Hatton".
The competition within the ring matched the sentiment. Arthur was sent to the canvas by a left hook squarely on the chin in the early round, standing uncertainly to his feet on the referee's count.
But the red-colored attire of Arthur soon came forward again. On the opposite side, the opponent - in competitive blue - was marked up soon, heavy swelling appearing under his face as the pair exchanged punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the result with scoring tallies of draw, narrow lead and wider gap, but both fighters were relentless and courageous, exactly what their idol the legend embodied.
