British light heavyweight Joshua Buatsi earned a win yet disappointing start to life under fresh promotional backing with a unanimous decision over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a split decision in a tight ten-round bout at the Manchester venue.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the styles didn't complement each other, with frequent clinching marring the action.
The scoring judges had it 96-94 to the winner, with the final judge a 95-95.
"It wasn't my finest showing but how do champions respond? They prevail," the victor commented in the ring as he was met by disapproval from the spectators.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Various analysts felt Parker, thirty-one, merited the win but the British boxer suffered the second setback of his 28-fight professional journey.
The Champion Secures Win in Dull Affair
His career development has stalled in the past few years through contract problems and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He opened tentatively, with both competitors willing to be aggressive in a tentative opening few rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, creating difficulties for Buatsi, who operated with a protective stance to barely take the cleaner periods.
The audience's tolerance decreased during regular grabbing, with the challenger going down multiple occasions during grappling.
The underdog closed well, but several stanzas were hard to judge. Nevertheless, former world champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian champion Bivol dominating the weight class, the road to world glory - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Contest
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a terrific local rivalry contest to secure the European light-heavyweight belt.
The stadium fell silent for a deeply poignant homage before the fight as a bell ceremony tolled in honor of the city's native Hatton, who died 46 years old in September.
It was the first major televised match card in the city since the passing of Hatton. As the last bell faded, the quiet transitioned to a shout of "there's only one Hatton".
The fighting within the ring equaled the emotion. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, rising shakily to his feet on the count of eight.
But the red-colored attire of Arthur soon advanced again. From the other corner, Rea - in competitive blue - was marked up quickly, significant bruising appearing under his orbital area as the duo exchanged hard punches.
Rea, 27, delivered effective strikes but the champion, 34, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
The victor edged the verdict with official scores of 114-114, 115-113 and 115-112, but both fighters were persistent and courageous, all the qualities their idol the legend represented.
