UK light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's punch output likely gained him a majority decision in a close 10-round fight at the Manchester venue.
But Parker had his moments, delivering effective clean blows in a contest where the approaches failed to mesh, with constant grabbing spoiling the contest.
The scoring judges judged it 96-94 in favor to the winner, with the remaining official a 95-95 draw.
"It wasn't my greatest showing but how do champions respond? They prevail," Buatsi commented in the ring as he was met by negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an memorable fight with Callum Smith in February - to claim a twentieth professional win.
Several boxing experts thought the challenger, thirty-one, should have been awarded the decision but the Derbyshire fighter suffered the second defeat of his 28-bout career.
The Champion Earns Triumph in Dull Encounter
Buatsi's progress has slowed in recent times through management issues and extended periods of inactivity.
Once tipped as the rising talent of UK boxing, he now is positioned trying to achieve expectations - maybe in what seems like a ultimate opportunity - under new promotional backing.
He began cautiously, with both competitors willing to be aggressive in a calculated opening few rounds.
Parker, whose only previous defeat came at super-middleweight against John Ryder in 2022 after breaking his hand mid-fight, was making just his second appearance at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who worked behind a solid defense to narrowly win the more effective rounds.
The crowd's patience decreased during frequent holding, with the challenger slipping to the canvas several times during clinches.
The underdog ended stronger, but multiple periods were hard to judge. However, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Tribute Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur overcame Bradley Rea by close verdict in a outstanding local rivalry fight to win the European light-heavyweight title.
The arena grew hushed for a profoundly moving tribute prior to the bout as ten bells sounded in honor of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised boxing event in the city since Hatton's passing. As the final chime disappeared, the stillness became a roar of "there's only one Ricky Hatton".
The action within the ring matched the emotion. The eventual winner was floored by a left hook squarely on the face in the initial stage, rising shakily to his feet on the count of eight.
But the traditional red equipment of Arthur soon came forward again. On the opposite side, Rea - in competitive blue - was damaged quickly, noticeable damage forming under his eye as the fighters exchanged hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace seldom decreased over the full distance.
Arthur edged the decision with judges scorecards of 114-114, close margin and clearer margin, but both fighters were persistent and brave, exactly what their hero Hatton stood for.
