British light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a judges' verdict in a tight ten-round bout at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a match where the approaches failed to mesh, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 to the winner, with the third a 95-95.
"It wasn't my greatest performance but how do champions respond? They win," the victor stated in the ringside as he was greeted with negative reactions from the spectators.
The British fighter bounced back after his first professional defeat - an epic battle with his previous opponent in last winter - to secure a twentieth professional win.
Various analysts believed the challenger, 31, deserved the win but the Derbyshire fighter endured the second loss of his 28-bout professional journey.
The Champion Secures Triumph in Slow Encounter
His career development has plateaued in the past few years through management issues and considerable time of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a last chance - under new promotional backing.
He started carefully, with neither fighter willing to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after damaging his hand during the bout, was participating in his second bout at light-heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The audience's tolerance decreased during frequent holding, with Parker going down several times during grappling.
The underdog finished the stronger, but multiple periods were challenging to assess. Nevertheless, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for Parker, awarding Buatsi just one round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Hatton Memorial Inspires All-Manchester Contest
In the secondary fight, Arthur beat Bradley Rea by split-decision in a excellent all-Manchester fight to capture the continental belt.
The stadium grew hushed for a extremely emotional tribute ahead of the contest as ten bells tolled in memory of the city's native Hatton, who passed away aged 46 in recently.
It was the first major televised fight night in the city since Hatton's death. As the concluding sound faded, the stillness became a chant of "there's only one Ricky Hatton".
The fighting inside the ropes equaled the feeling. Arthur was knocked down by a powerful punch flush on the face in the second round, rising shakily to his feet on the count of eight.
But the Manchester United-red attire of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was damaged early, significant bruising forming under his face as the duo exchanged powerful shots.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with effective uppercuts as the intensity seldom decreased over twelve rounds.
The victor barely secured the decision with scoring tallies of draw, narrow lead and clearer margin, but both fighters were relentless and courageous, exactly what their inspiration Hatton represented.
