British light-heavyweight Joshua Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a split decision in a competitive ten-round bout at the boxing arena.
But Parker found success, delivering effective single shots in a fight where the styles never quite clicked, with constant grabbing spoiling the fight.
The scoring judges judged it 96-94 in favor to the winner, with the third a 95-95 draw.
"It wasn't my finest display but how do champions respond? They win," Buatsi said in the ring as he was greeted with boos from the audience.
The Londoner bounced back after his maiden career setback - an memorable fight with his previous opponent in February - to earn a 20th pro success.
Various analysts believed the challenger, thirty-one, should have been awarded the victory but the contender experienced the second setback of his 28-fight career.
Buatsi Claims Win in Slow Match
Buatsi's progress has plateaued in the past few years through contract problems and long spells of inactivity.
Earlier forecast as the next star of the British fight scene, he now stands trying to fulfil that early promise - perhaps in what seems like a final roll of the dice - under recent support.
He began cautiously, with neither fighter ready to take risks in a calculated early stages.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was participating in his second fight at light-heavyweight.
By the middle rounds, Parker had kept it close, making life awkward for the favorite, who utilized a tight guard to barely take the more effective rounds.
The crowd's patience decreased amid frequent holding, with the challenger slipping to the canvas various instances during close exchanges.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, former world champion Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just one round.
The victor advances, but with the likes of hard hitter David Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Hatton Memorial Fuels All-Manchester Fight
In the secondary fight, Arthur beat Bradley Rea by close verdict in a terrific all-Manchester fight to secure the continental championship.
The venue fell silent for a deeply poignant tribute before the fight as ten bells tolled in honor of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the initial significant broadcast boxing event in the location since the passing of Hatton. As the last bell disappeared, the stillness became a shout of "there's only one Ricky Hatton".
The competition during the bout reflected the sentiment. Arthur was floored by a powerful punch squarely on the face in the second round, getting up unsteadily to his position on the eight count.
But the Manchester United-red equipment of the fighter soon came forward again. Across the ring, Rea - in opposing blue - was marked up early, significant bruising appearing under his orbital area as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but the champion, thirty-four, fought fire with fire with effective uppercuts as the action rarely dropped over twelve rounds.
Arthur barely secured the result with scoring tallies of even score, narrow lead and 115-112, but the two athletes were relentless and courageous, exactly what their hero Hatton represented.
