UK light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a split decision in a close 10-round contest at the Manchester venue.
But the challenger landed significant shots, connecting with powerful single shots in a fight where the approaches didn't complement each other, with frequent clinching spoiling the contest.
Two judges scored it 96-94 to the winner, with the third a 95-95 draw.
"It wasn't my finest display but how do champions respond? They prevail," Buatsi said in the ring as he was met by disapproval from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to secure a twentieth professional win.
Various analysts thought the challenger, 31, merited the win but the Derbyshire fighter experienced the second defeat of his 28-fight career.
Buatsi Earns Triumph in Uneventful Match
The fighter's advancement has stalled in the past few years through management issues and long spells of inactivity.
Previously predicted as the future of the British fight scene, he now finds himself trying to achieve expectations - perhaps in what appears to be a ultimate opportunity - under fresh management.
He started carefully, with the two boxers prepared to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in 2022 after damaging his hand mid-fight, was participating in his second fight at light-heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for Buatsi, who utilized a protective stance to narrowly win the better periods.
The spectators' acceptance wore thin amid constant clinching, with Parker falling to the floor several times during clinches.
The underdog finished the stronger, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian star Bivol ruling the division, the journey to titles - on this evidence - still appears challenging.
Hatton Tribute Motivates Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a outstanding all-Manchester battle to win the continental title.
The arena grew hushed for a deeply poignant tribute ahead of the contest as ten bells tolled in honor of Manchester's own Ricky Hatton, who died at age 46 in last month.
It was the first major televised match card in the urban center since Hatton's death. As the final chime disappeared, the stillness became a shout of "only one Ricky Hatton".
The fighting inside the ropes equaled the feeling. Arthur was knocked down by a significant blow directly to the jaw in the initial stage, getting up unsteadily to his feet on the count of eight.
But the traditional red attire of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was injured early, heavy swelling appearing under his orbital area as the pair traded punishing blows.
The challenger, twenty-seven, landed power punches but the champion, 34, responded in kind with powerful upward punches as the action seldom decreased over 12 rounds.
Arthur narrowly won the decision with judges scorecards of draw, 115-113 and clearer margin, but both fighters were persistent and brave, everything their hero the legend stood for.
