British light heavyweight Joshua Buatsi earned a win yet disappointing start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a judges' verdict in a close ten-round contest at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a fight where the techniques failed to mesh, with constant grabbing marring the contest.
Two judges judged it 96-94 in favor to the winner, with the third a 95-95.
"It wasn't my best showing but how do champions respond? They succeed," the victor stated in the ringside as he was faced boos from the crowd.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to secure a twentieth professional win.
Various analysts felt Parker, thirty-one, merited the decision but the contender experienced the second loss of his 28-fight career.
Buatsi Claims Triumph in Dull Encounter
Buatsi's progress has slowed in recent times through management issues and extended periods of lack of fights.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to fulfil that early promise - perhaps in what feels like a final roll of the dice - under new promotional backing.
He started carefully, with the two boxers ready to overcommit in a cagey initial rounds.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand mid-fight, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, creating difficulties for the favorite, who worked behind a protective stance to edge the cleaner periods.
The audience's tolerance diminished because of regular grabbing, with the challenger going down several times during grappling.
Parker ended stronger, but many rounds were hard to judge. However, ex-champion Carl Frampton - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor advances, but with the caliber of power puncher David Benavidez, and Russian star Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Ricky Hatton Tribute Fuels Manchester Derby Contest
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a excellent Manchester vs Manchester fight to secure the continental belt.
The stadium grew hushed for a extremely emotional homage prior to the bout as 10 bells tolled in honor of the city's native Hatton, who passed away at age 46 in September.
It was the premier televised fight night in the location since Hatton's passing. As the final chime ended, the stillness became a chant of "only one Hatton".
The fighting during the bout equaled the feeling. Arthur was floored by a significant blow flush on the chin in the initial stage, rising shakily to his position on the eight count.
But the traditional red attire of Arthur soon pressed ahead again. On the opposite side, the opponent - in competitive blue - was marked up soon, significant bruising forming under his orbital area as the fighters landed punishing blows.
The challenger, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
Arthur barely secured the decision with official scores of draw, close margin and wider gap, but both fighters were relentless and full of heart, everything their inspiration Hatton embodied.
