UK light heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a tight 10-round contest at the Co-op Live Arena.
But the challenger landed significant shots, landing some telling single shots in a match where the approaches failed to mesh, with excessive holding spoiling the fight.
Two judges scored it 96-94 for to Buatsi, with the remaining official a 95-95.
"It wasn't my best showing but what do champions do? They succeed," Buatsi commented in the ringside as he was faced negative reactions from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers believed Parker, 31, should have been awarded the victory but the Derbyshire fighter suffered the second loss of his 28-bout professional journey.
Buatsi Secures Win in Slow Affair
His career development has stalled in the past few years through contract problems and extended periods of inactivity.
Earlier forecast as the future of the British fight scene, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He opened tentatively, with neither fighter willing to overcommit in a tentative initial rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, making life awkward for Buatsi, who worked behind a protective stance to barely take the more effective rounds.
The audience's tolerance decreased during frequent holding, with Parker slipping to the canvas multiple occasions during grappling.
The underdog ended stronger, but many rounds were hard to judge. Although, former world champion Carl Frampton - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - judging by this showing - still appears challenging.
Hatton Tribute Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific local rivalry battle to secure the European light-heavyweight championship.
The stadium fell silent for a profoundly moving homage before the fight as ten bells sounded in honor of the city's native Ricky Hatton, who succumbed at age 46 in recently.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the last bell ended, the stillness gave way to a roar of "there's just one Ricky Hatton".
The fighting within the ring reflected the feeling. The eventual winner was sent to the canvas by a left hook flush on the chin in the early round, rising shakily to his position on the count of eight.
But the Manchester United-red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was damaged quickly, significant bruising developing under his face as the duo traded hard punches.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, matched the intensity with effective uppercuts as the action seldom decreased over twelve rounds.
Arthur barely secured the decision with scoring tallies of even score, narrow lead and wider gap, but the two athletes were persistent and courageous, all the qualities their hero the legend stood for.
