UK light-heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's work rate likely gained him a majority decision in a tight 10-round bout at the Co-op Live Arena.
But Parker found success, landing some telling individual punches in a contest where the techniques didn't complement each other, with frequent clinching marring the contest.
The officials judged it 96-94 for to Buatsi, with the third a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They succeed," Buatsi said in the ring as he was faced negative reactions from the crowd.
The Londoner bounced back after his initial pro loss - an memorable fight with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers felt Parker, 31, should have been awarded the victory but the Derbyshire fighter suffered the second loss of his 28-bout career.
The Champion Earns Win in Dull Match
The fighter's advancement has slowed in the past few years through promotional disputes and considerable time of lack of fights.
Earlier forecast as the next star of British boxing, he now is positioned trying to achieve expectations - possibly in what seems like a ultimate opportunity - under fresh management.
He began cautiously, with both competitors ready to take risks in a calculated early stages.
Parker, whose sole prior loss came at super middleweight against John Ryder in 2022 after suffering a hand injury in the contest, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, making life awkward for the favorite, who worked behind a protective stance to barely take the cleaner stanzas.
The audience's tolerance wore thin amid regular grabbing, with the challenger falling to the floor several times during clinches.
Parker ended stronger, but several stanzas were hard to judge. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just a single round.
The victor advances, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Homage Fuels All-Manchester Battle
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a outstanding Manchester vs Manchester fight to secure the European light heavyweight belt.
The arena became quiet for a deeply poignant memorial prior to the bout as ten bells sounded in remembrance of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised fight night in the urban center since Hatton's death. As the last bell faded, the quiet gave way to a shout of "there's only one Ricky Hatton".
The competition within the ring equaled the sentiment. Arthur was sent to the canvas by a significant blow directly to the chin in the early round, rising shakily to his position on the referee's count.
But the Manchester United-red shorts of Arthur soon advanced again. On the opposite side, the opponent - in competitive blue - was damaged early, heavy swelling forming under his eye as the fighters landed powerful shots.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity hardly diminished over the full distance.
The victor narrowly won the decision with official scores of even score, 115-113 and wider gap, but the two athletes were persistent and full of heart, everything their hero the legend embodied.
