UK light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's activity level likely gained him a judges' verdict in a tight ten-round fight at the Co-op Live Arena.
But the challenger found success, landing some telling clean blows in a fight where the approaches failed to mesh, with frequent clinching marring the contest.
Two judges scored it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my finest display but how do champions respond? They succeed," the victor stated in the ringside as he was faced boos from the crowd.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Several boxing experts thought the challenger, 31, deserved the victory but the contender suffered the second setback of his 28-bout professional journey.
The Champion Earns Win in Dull Match
Buatsi's progress has plateaued in the past few years through contract problems and considerable time of inactivity.
Once tipped as the rising talent of UK boxing, he now finds himself trying to achieve expectations - maybe in what seems like a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to overcommit in a cagey initial rounds.
Parker, whose sole prior loss came at the lower weight class against his former opponent in two years ago after breaking his hand mid-fight, was making just his second appearance at the higher weight class.
By the middle rounds, the underdog had stayed in contention, causing problems for the favorite, who worked behind a protective stance to edge the more effective stanzas.
The spectators' acceptance diminished amid regular grabbing, with Parker slipping to the canvas several times during clinches.
Parker closed well, but several stanzas were hard to judge. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, giving Buatsi just only one stanza.
Buatsi progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Dmitry Bivol leading the category, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Contest
In the supporting bout, Arthur beat Bradley Rea by close verdict in a excellent all-Manchester battle to capture the European light heavyweight title.
The arena became quiet for a profoundly moving tribute prior to the bout as a bell ceremony sounded in remembrance of local hero Ricky Hatton, who succumbed aged 46 in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the last bell faded, the stillness gave way to a shout of "there's just one Ricky Hatton".
The action within the ring matched the emotion. Arthur was floored by a left hook directly to the chin in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored equipment of Arthur soon pressed ahead again. On the opposite side, Rea - in rival City blue - was damaged quickly, heavy swelling forming under his face as the fighters traded punishing blows.
Rea, twenty-seven, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor edged the decision with scoring tallies of even score, close margin and wider gap, but each competitor were persistent and courageous, all the qualities their hero Hatton represented.
