British light-heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a split decision in a close 10-round contest at the Co-op Live Arena.
But the challenger had his moments, delivering effective individual punches in a match where the styles failed to mesh, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 for to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest performance but how do champions respond? They prevail," Buatsi said in the ringside as he was met by negative reactions from the spectators.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Various analysts thought Parker, thirty-one, should have been awarded the win but the Derbyshire fighter endured the second loss of his 28-match career.
The Champion Secures Win in Dull Encounter
Buatsi's progress has slowed in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what feels like a final roll of the dice - under recent support.
He opened tentatively, with neither fighter willing to be aggressive in a cagey initial rounds.
Parker, whose single earlier setback came at the lower weight class against John Ryder in 2022 after breaking his hand in the contest, was making just his second bout at light-heavyweight.
By the middle rounds, Parker had made it competitive, causing problems for the favorite, who worked behind a tight guard to narrowly win the more effective rounds.
The audience's tolerance diminished during constant clinching, with Parker falling to the floor several times during grappling.
The underdog finished the stronger, but many rounds were hard to judge. Nevertheless, former world champion Carl Frampton - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Bivol ruling the division, the path to championship success - based on this performance - still looks steep.
Ricky Hatton Homage Fuels Manchester Derby Battle
In the supporting bout, Arthur overcame Bradley Rea by divided decision in a excellent Manchester vs Manchester battle to capture the European light-heavyweight belt.
The venue fell silent for a deeply poignant homage prior to the bout as 10 bells rang in memory of the city's native Hatton, who passed away 46 years old in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the final chime disappeared, the silence transitioned to a chant of "there's just one Ricky Hatton".
The action during the bout matched the emotion. Arthur was floored by a powerful punch flush on the chin in the early round, rising shakily to his footing on the referee's count.
But the red-colored shorts of Arthur soon advanced again. On the opposite side, the opponent - in rival City blue - was injured soon, heavy swelling appearing under his eye as the duo exchanged hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, responded in kind with stinging uppercuts as the action rarely dropped over the full distance.
Arthur edged the verdict with scoring tallies of draw, 115-113 and clearer margin, but both fighters were persistent and brave, everything their idol the legend stood for.
