British light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to his career under recent management with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a judges' verdict in a tight 10-round bout at the Manchester venue.
But the challenger had his moments, connecting with powerful single shots in a contest where the techniques never quite clicked, with constant grabbing marring the contest.
Two judges judged it 96-94 in favor to the winner, with the remaining official a even score.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi commented in the arena as he was greeted with boos from the audience.
The Londoner got back to winning after his initial pro loss - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts thought the challenger, 31, deserved the win but the contender endured the second defeat of his 28-match professional journey.
The Champion Secures Win in Slow Match
The fighter's advancement has stalled in recent times through management issues and extended periods of lack of fights.
Once tipped as the future of the British fight scene, he now stands trying to realize his potential - perhaps in what appears to be a final roll of the dice - under fresh management.
He began cautiously, with neither fighter ready to overcommit in a tentative 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 bout at light-heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who utilized a protective stance to narrowly win the better rounds.
The audience's tolerance decreased during regular grabbing, with Parker going down multiple occasions during grappling.
Parker finished the stronger, but multiple periods were challenging to assess. However, previous titleholder the boxing analyst - providing analysis for the broadcast network - had it significantly in favor for Parker, awarding Buatsi just a single round.
The victor progresses, but with the caliber of heavy hitter David Benavidez, and Russian star Bivol leading the category, the road to world glory - on this evidence - still appears challenging.
Hatton Memorial Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific local rivalry fight to win the European light heavyweight championship.
The venue fell silent for a profoundly moving homage prior to the bout as ten bells sounded in remembrance of Manchester's own Ricky Hatton, who died at age 46 in recently.
It was the premier televised fight night in the urban center since the passing of Hatton. As the concluding sound disappeared, the stillness became a roar of "there's just one Hatton".
The action during the bout matched the feeling. The eventual winner was sent to the canvas by a powerful punch flush on the chin in the early round, rising shakily to his feet on the eight count.
But the red-colored attire of the fighter soon pressed ahead again. On the opposite side, the opponent - in opposing blue - was damaged early, heavy swelling forming under his face as the fighters landed hard punches.
Rea, twenty-seven, connected with strong blows but the champion, 34, responded in kind with powerful upward punches as the intensity seldom decreased over 12 rounds.
The victor edged the result with official scores of 114-114, 115-113 and wider gap, but the two athletes were determined and courageous, all the qualities their hero Hatton represented.
