British light heavyweight Joshua Buatsi made a winning yet disappointing start to life under new promoters with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a competitive ten-round bout at the Manchester venue.
But Parker landed significant shots, delivering effective individual punches in a match where the styles failed to mesh, with frequent clinching marring the action.
Two judges scored it 96-94 in favor to the winner, with the final judge a 95-95.
"It wasn't my best showing but what defines champions? They win," the victor commented in the arena as he was faced disapproval from the audience.
The British fighter bounced back after his maiden career setback - an memorable fight with Callum Smith in last winter - to earn a 20th pro success.
Various analysts thought the challenger, 31, deserved the decision but the Derbyshire fighter experienced the second defeat of his 28-bout career.
The Champion Claims Triumph in Dull Encounter
His career development has plateaued in recent years through contract problems and long spells of inactivity.
Previously predicted as the next star of British boxing, he now finds himself trying to achieve expectations - maybe in what feels like a final roll of the dice - under recent support.
He began cautiously, with the two boxers prepared to overcommit in a tentative initial rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after damaging his hand during the bout, was competing in only his second fight at light-heavyweight.
By the middle rounds, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to narrowly win the cleaner stanzas.
The audience's tolerance diminished amid regular grabbing, with Parker slipping to the canvas various instances during clinches.
Parker finished the stronger, but many rounds were challenging to assess. However, ex-champion the boxing analyst - providing analysis for Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor advances, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still looks steep.
Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Arthur defeated Bradley Rea by close verdict in a outstanding local rivalry contest to secure the European light-heavyweight belt.
The venue grew hushed for a deeply poignant memorial prior to the bout as 10 bells rang in remembrance of the city's native Ricky Hatton, who died 46 years old in September.
It was the first major televised boxing event in the urban center since the passing of Hatton. As the last bell faded, the stillness gave way to a chant of "there's only one Hatton".
The action during the bout matched the feeling. The eventual winner was knocked down by a powerful punch flush on the jaw in the second round, rising shakily to his position on the referee's count.
But the red-colored attire of the fighter soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up soon, heavy swelling appearing under his eye as the duo landed powerful shots.
The challenger, twenty-seven, delivered effective strikes but the champion, 34, responded in kind with stinging uppercuts as the pace seldom decreased over 12 rounds.
Arthur narrowly won the decision with scoring tallies of 114-114, narrow lead and wider gap, but the two athletes were persistent and courageous, exactly what their idol the legend stood for.
