UK light heavyweight Joshua Buatsi secured a victory yet underwhelming debut to his career under recent management with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a tight ten-round fight at the Manchester venue.
But Parker landed significant shots, delivering effective individual punches in a fight where the techniques never quite clicked, with constant grabbing marring the action.
Two judges scored it 96-94 for to the winner, with the remaining official a even score.
"It wasn't my best showing but how do champions respond? They prevail," the victor said in the ring as he was greeted with negative reactions from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts thought Parker, thirty-one, merited the victory but the British boxer suffered the second setback of his 28-bout career.
The Champion Earns Win in Dull Match
The fighter's advancement has plateaued in recent years through management issues and considerable time of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what feels like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors prepared to overcommit in a cagey initial rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for the favorite, who utilized a solid defense to barely take the better rounds.
The audience's tolerance decreased amid frequent holding, with the challenger slipping to the canvas various instances during close exchanges.
The underdog closed well, but many rounds were challenging to assess. However, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, awarding Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter David Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Hatton Memorial Inspires All-Manchester Contest
In the supporting bout, Arthur defeated Rea by close verdict in a outstanding all-Manchester battle to win the European light-heavyweight belt.
The arena grew hushed for a deeply poignant memorial ahead of the contest as 10 bells tolled in honor of the city's native Hatton, who passed away 46 years old in recently.
It was the first major televised boxing event in the location since the passing of Hatton. As the concluding sound ended, the stillness transitioned to a roar of "there's just one Hatton".
The competition inside the ropes reflected the emotion. Arthur was sent to the canvas by a significant blow squarely on the face in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red equipment of Arthur soon came forward again. From the other corner, Rea - in rival City blue - was marked up quickly, noticeable damage forming under his orbital area as the duo traded powerful shots.
Rea, twenty-seven, landed power punches but the champion, 34, fought fire with fire with stinging uppercuts as the action seldom decreased over the full distance.
The victor narrowly won the verdict with scoring tallies of 114-114, close margin and 115-112, but each competitor were determined and courageous, exactly what their hero Hatton represented.
