UK light heavyweight Joshua Buatsi secured a victory yet unimpressive start to his career under fresh promotional backing with a unanimous decision over Parker in Manchester.
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 landed significant shots, delivering effective clean blows in a contest where the styles never quite clicked, with constant grabbing spoiling the contest.
Two judges had it 96-94 to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest display but how do champions respond? They win," the victor stated in the arena as he was met by boos from the spectators.
The British fighter returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to secure a 20th pro success.
Some ringside observers felt the challenger, 31, deserved the victory but the British boxer experienced the second defeat of his 28-match professional journey.
The Champion Claims Win in Dull Encounter
The fighter's advancement has stalled in recent years through contract problems and extended periods of inactivity.
Once tipped as the future of the British fight scene, he now is positioned trying to achieve expectations - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with both competitors ready to take risks in a calculated early stages.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at the higher weight class.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who operated with a protective stance to edge the more effective rounds.
The audience's tolerance wore thin because of frequent holding, with Parker going down several times during grappling.
The underdog finished the stronger, but multiple periods were hard to judge. However, former world champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, giving Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol ruling the division, the path to championship success - based on this performance - still appears challenging.
Hatton Homage Inspires Manchester Derby Contest
In the secondary fight, Lyndon Arthur beat Bradley Rea by split-decision in a excellent local rivalry battle to capture the European light-heavyweight championship.
The arena became quiet for a extremely emotional homage before the fight as ten bells rang in remembrance of local hero Hatton, who died at age 46 in last month.
It was the first major televised match card in the location since the passing of Hatton. As the concluding sound ended, the quiet gave way to a roar of "there's only one Ricky Hatton".
The competition during the bout reflected the sentiment. Arthur was sent to the canvas by a powerful punch directly to the jaw in the second round, standing uncertainly to his feet on the eight count.
But the red-colored shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged early, noticeable damage appearing under his eye as the pair traded hard punches.
The challenger, twenty-seven, landed power punches but Arthur, 34, responded in kind with stinging uppercuts as the pace rarely dropped over twelve rounds.
Arthur barely secured the result with official scores of 114-114, narrow lead and 115-112, but both fighters were persistent and courageous, everything their hero Hatton represented.
