British light heavyweight Joshua Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a tight ten-round fight at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a match where the styles failed to mesh, with constant grabbing marring the fight.
The officials had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best display but what defines champions? They succeed," Buatsi commented in the ring as he was met by disapproval from the crowd.
The British fighter bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers felt Parker, 31, deserved the win but the contender suffered the second loss of his 28-fight career.
The Champion Secures Win in Slow Affair
His career development has plateaued in recent years through contract problems and extended periods of inactivity.
Previously predicted as the future of the British fight scene, he now stands trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under new promotional backing.
He started carefully, with neither fighter prepared to take risks in a calculated initial rounds.
Parker, whose single earlier setback came at the lower weight class against his former opponent in two years ago after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who utilized a protective stance to barely take the more effective periods.
The crowd's patience decreased amid frequent holding, with Parker going down various instances during grappling.
Parker closed well, but multiple periods were challenging to assess. Although, ex-champion Carl Frampton - working with the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
Buatsi progresses, but with the likes of hard hitter David Benavidez, and Russian champion Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Inspires All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a terrific Manchester vs Manchester contest to win the continental belt.
The venue fell silent for a deeply poignant tribute ahead of the contest as ten bells rang in honor of the city's native Ricky Hatton, who passed away at age 46 in last month.
It was the first major televised fight night in the location since Hatton's passing. As the last bell disappeared, the quiet transitioned to a roar of "there's only one Ricky Hatton".
The action within the ring matched the emotion. Arthur was floored by a powerful punch flush on the jaw in the second round, getting up unsteadily to his position on the eight count.
But the Manchester United-red attire of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising forming under his eye as the duo exchanged punishing blows.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with effective uppercuts as the action seldom decreased over twelve rounds.
The victor barely secured the result with judges scorecards of 114-114, 115-113 and 115-112, but each competitor were relentless and full of heart, all the qualities their inspiration Hatton represented.
