British light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a competitive ten-round bout at the Manchester venue.
But the challenger found success, delivering effective single shots in a match where the styles never quite clicked, with frequent clinching marring the contest.
Two judges scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my finest display but how do champions respond? They win," the victor commented in the ring as he was faced negative reactions from the audience.
The British fighter bounced back after his first professional defeat - an epic battle with Callum Smith in last winter - to claim a twentieth professional win.
Various analysts thought the challenger, 31, deserved the decision but the Derbyshire fighter suffered the second loss of his 28-fight career.
The Champion Claims Win in Dull Encounter
The fighter's advancement has slowed in recent times through promotional disputes and long spells of inactivity.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to realize his potential - perhaps in what seems like a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter willing to be aggressive in a tentative initial rounds.
The challenger, whose sole prior loss came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was competing in only his second bout at light heavyweight.
By the halfway stage, the underdog had kept it close, making life awkward for Buatsi, who worked behind a solid defense to edge the more effective stanzas.
The crowd's patience decreased because of constant clinching, with Parker falling to the floor several times during grappling.
The underdog finished the stronger, but several stanzas were challenging to assess. Although, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the likes of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Homage Motivates All-Manchester Fight
In the supporting bout, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester battle to secure the continental belt.
The venue grew hushed for a profoundly moving tribute prior to the bout as 10 bells sounded in honor of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the first major televised match card in the location since Hatton's passing. As the final chime disappeared, the quiet gave way to a chant of "only one Ricky Hatton".
The action inside the ropes equaled the emotion. Arthur was knocked down by a significant blow flush on the chin in the initial stage, standing uncertainly to his position on the eight count.
But the traditional red shorts of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was injured quickly, noticeable damage appearing under his orbital area as the fighters landed punishing blows.
The challenger, 27, delivered effective strikes but the champion, thirty-four, responded in kind with powerful upward punches as the action rarely dropped over the full distance.
The victor barely secured the decision with scoring tallies of 114-114, 115-113 and clearer margin, but both fighters were persistent and courageous, everything their hero Hatton represented.
