UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a judges' verdict in a close 10-round contest at the Co-op Live Arena.
But the challenger found success, landing some telling individual punches in a fight where the styles failed to mesh, with excessive holding marring the contest.
The officials scored it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my greatest performance but what defines champions? They succeed," the victor said in the ring as he was faced negative reactions from the crowd.
The British fighter returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in last winter - to secure a twentieth professional win.
Various analysts thought the challenger, 31, should have been awarded the victory but the Derbyshire fighter endured the second defeat of his 28-bout professional journey.
The Champion Earns Triumph in Slow Affair
Buatsi's progress has slowed in recent years through contract problems and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to realize his potential - maybe in what seems like a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers willing to take risks in a calculated early stages.
Parker, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was making just his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, making life awkward for the favorite, who worked behind a solid defense to narrowly win the better stanzas.
The audience's tolerance decreased amid constant clinching, with Parker slipping to the canvas various instances during clinches.
Parker finished the stronger, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - commentating on Dazn - had it significantly in favor for Parker, giving Buatsi just only one stanza.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Memorial Motivates Manchester Derby Battle
In the supporting bout, Arthur beat Bradley Rea by divided decision in a terrific all-Manchester contest to capture the European light-heavyweight belt.
The arena fell silent for a profoundly moving homage before the fight as 10 bells rang in memory of the city's native Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the city since Hatton's death. As the last bell faded, the silence became a chant of "only one Ricky Hatton".
The competition during the bout matched the feeling. Arthur was sent to the canvas by a significant blow flush on the face in the second round, getting up unsteadily to his feet on the referee's count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured soon, significant bruising forming under his orbital area as the duo landed powerful shots.
The challenger, twenty-seven, connected with strong blows but the champion, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over the full distance.
The victor barely secured the result with judges scorecards of even score, 115-113 and 115-112, but each competitor were relentless and brave, exactly what their idol the legend stood for.
