UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under recent management 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 ten-round bout at the boxing arena.
But Parker had his moments, landing some telling clean blows in a match where the styles never quite clicked, with constant grabbing marring the fight.
The officials scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my finest display but what do champions do? They succeed," Buatsi said in the ringside as he was met by boos from the spectators.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th pro success.
Some ringside observers felt Parker, thirty-one, merited the decision but the Derbyshire fighter suffered the second defeat of his 28-bout career.
Buatsi Claims Triumph in Dull Encounter
The fighter's advancement has stalled in the past few years through management issues and long spells of lack of fights.
Previously predicted as the next star of the British fight scene, he now finds himself trying to achieve expectations - possibly in what appears to be a last chance - under new promotional backing.
He began cautiously, with neither fighter ready to be aggressive in a tentative initial rounds.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second bout at the higher weight class.
By the fight's midpoint, the underdog had stayed in contention, causing problems for the favorite, who worked behind a solid defense to narrowly win the cleaner rounds.
The crowd's patience wore thin during regular grabbing, with the challenger slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. However, former world champion the boxing analyst - working with Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor advances, but with the presence of heavy hitter David Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by close verdict in a excellent local rivalry fight to win the European light heavyweight belt.
The stadium became quiet for a profoundly moving tribute prior to the bout as 10 bells tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in last month.
It was the initial significant broadcast fight night in the urban center since Hatton's death. As the last bell disappeared, the silence gave way to a shout of "there's only one Ricky Hatton".
The action within the ring equaled the emotion. Arthur was floored by a significant blow flush on the jaw in the early round, standing uncertainly to his footing on the referee's count.
But the traditional red equipment of Arthur soon came forward again. Across the ring, the opponent - in rival City blue - was injured early, heavy swelling developing under his orbital area as the fighters landed powerful shots.
The challenger, 27, landed power punches but the champion, 34, matched the intensity with powerful upward punches as the action seldom decreased over 12 rounds.
The victor narrowly won the decision with scoring tallies of 114-114, close margin and clearer margin, but both fighters were relentless and full of heart, everything their hero the legend stood for.
