British light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a split decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the styles never quite clicked, with constant grabbing marring the fight.
Two judges scored it 96-94 in favor to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They prevail," the victor commented in the ringside as he was met by disapproval from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to earn a 20th career victory.
Some ringside observers thought Parker, 31, deserved the victory but the British boxer endured the second setback of his 28-fight career.
Buatsi Secures Triumph in Uneventful Encounter
His career development has slowed in the past few years through promotional disputes and considerable time of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a final roll of the dice - under recent support.
He began cautiously, with neither fighter prepared to overcommit in a tentative opening few rounds.
The challenger, whose sole prior loss 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 stayed in contention, creating difficulties for Buatsi, who operated with a solid defense to narrowly win the more effective stanzas.
The crowd's patience decreased because of constant clinching, with Parker going down several times during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of hard hitter David Benavidez, and Eastern European fighter Bivol leading the category, the road to world glory - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels All-Manchester Contest
In the secondary fight, Arthur overcame Bradley Rea by split-decision in a excellent all-Manchester battle to capture the European light heavyweight belt.
The stadium grew hushed for a profoundly moving tribute ahead of the contest as ten bells sounded in remembrance of Manchester's own Hatton, who passed away at age 46 in last month.
It was the first major televised fight night in the urban center since Hatton's death. As the last bell ended, the quiet gave way to a shout of "there's just one Hatton".
The competition within the ring equaled the feeling. Arthur was floored by a left hook directly to the jaw in the early round, rising shakily to his footing on the eight count.
But the traditional red attire of Arthur soon came forward again. From the other corner, the opponent - in competitive blue - was marked up soon, noticeable damage forming under his eye as the duo landed hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the intensity seldom decreased over the full distance.
The victor barely secured the verdict with judges scorecards of even score, close margin and wider gap, but the two athletes were persistent and full of heart, all the qualities their idol the legend embodied.
