UK light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a split decision in a competitive 10-round fight at the Manchester venue.
But the challenger landed significant shots, delivering effective clean blows in a contest where the styles failed to mesh, with frequent clinching spoiling the fight.
Two judges judged it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest showing but what do champions do? They win," Buatsi stated in the arena as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to earn a 20th career victory.
Several boxing experts thought Parker, 31, should have been awarded the win but the British boxer experienced the second defeat of his 28-match professional journey.
The Champion Secures Victory in Dull Encounter
His career development has stalled in recent times through contract problems and considerable time of lack of fights.
Once tipped as the rising talent of the British fight scene, he now stands trying to achieve expectations - possibly in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with neither fighter willing to take risks in a cagey early stages.
The challenger, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who utilized a protective stance to edge the cleaner rounds.
The spectators' acceptance decreased amid frequent holding, with the challenger falling to the floor several times during grappling.
The underdog finished the stronger, but many rounds were difficult to score. Although, ex-champion the boxing analyst - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the likes of power puncher David Benavidez, and Russian champion Bivol dominating the weight class, the journey to titles - on this evidence - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Battle
In the supporting bout, Arthur beat Bradley Rea by close verdict in a outstanding all-Manchester contest to secure the continental championship.
The arena fell silent for a profoundly moving memorial ahead of the contest as ten bells rang in memory of the city's native Ricky Hatton, who passed away 46 years old in September.
It was the initial significant broadcast match card in the location since Hatton's death. As the concluding sound disappeared, the stillness became a roar of "only one Ricky Hatton".
The fighting within the ring reflected the feeling. The eventual winner was knocked down by a significant blow squarely on the chin in the second round, standing uncertainly to his feet on the referee's count.
But the traditional red equipment of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was marked up quickly, significant bruising forming under his eye as the fighters landed punishing blows.
Rea, 27, connected with strong blows but the champion, 34, fought fire with fire with powerful upward punches as the action hardly diminished 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 determined and brave, exactly what their idol the legend stood for.
