UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to his career under new promoters with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate appeared to earn him a majority decision in a competitive 10-round fight at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the styles never quite clicked, with excessive holding spoiling the action.
Two judges judged it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my best performance but what do champions do? They succeed," Buatsi commented in the ringside as he was met by negative reactions from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers believed the challenger, thirty-one, deserved the victory but the Derbyshire fighter suffered the second defeat of his 28-fight career.
The Champion Secures Win in Uneventful Match
Buatsi's progress has stalled in recent years through contract problems and considerable time of lack of fights.
Earlier forecast as the rising talent of British boxing, he now stands trying to fulfil that early promise - perhaps in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers ready to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand during the bout, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who operated with a tight guard to narrowly win the more effective stanzas.
The spectators' acceptance wore thin during regular grabbing, with the challenger falling to the floor several times during grappling.
Parker ended stronger, but multiple periods were difficult to score. Nevertheless, previous titleholder Carl Frampton - commentating on Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by divided decision in a excellent all-Manchester contest to win the continental championship.
The arena fell silent for a deeply poignant memorial prior to the bout as ten bells sounded in honor of local hero Hatton, who passed away at age 46 in recently.
It was the initial significant broadcast fight night in the urban center since Hatton's passing. As the last bell faded, the silence transitioned to a chant of "there's just one Ricky Hatton".
The competition inside the ropes equaled the emotion. The eventual winner was sent to the canvas by a significant blow squarely on the chin in the early round, rising shakily to his feet on the referee's count.
But the red-colored equipment of Arthur soon advanced again. Across the ring, Rea - in rival City blue - was marked up quickly, noticeable damage forming under his face as the pair traded powerful shots.
Rea, 27, landed power punches but Arthur, 34, matched the intensity with stinging uppercuts as the action seldom decreased over 12 rounds.
Arthur narrowly won the result with scoring tallies of even score, 115-113 and wider gap, but the two athletes were relentless and brave, everything their idol the legend stood for.
