UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under new promoters with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight 10-round contest at the Co-op Live Arena.
But Parker found success, delivering effective clean blows in a match where the approaches didn't complement each other, with frequent clinching disrupting the fight.
The officials scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my finest showing but what do champions do? They succeed," Buatsi commented in the ringside as he was faced disapproval from the audience.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in last winter - to secure a twentieth professional win.
Some ringside observers believed the challenger, 31, merited the win but the British boxer suffered the second defeat of his 28-match career.
Buatsi Earns Triumph in Uneventful Encounter
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the future of UK boxing, he now is positioned trying to fulfil that early promise - maybe in what feels like a final roll of the dice - under fresh management.
He opened tentatively, with both competitors ready to be aggressive in a calculated initial rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the halfway stage, the underdog had kept it close, creating difficulties for Buatsi, who worked behind a solid defense to narrowly win the cleaner rounds.
The audience's tolerance decreased during frequent holding, with Parker going down various instances during grappling.
Parker finished the stronger, but many rounds were challenging to assess. Although, previous titleholder Carl Frampton - working with Dazn - had it strongly leaning for Parker, awarding Buatsi just only one stanza.
The victor progresses, but with the presence of power puncher Benavidez, and Russian champion Dmitry Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Hatton Memorial Fuels All-Manchester Contest
In the supporting bout, Lyndon Arthur defeated Rea by divided decision in a terrific all-Manchester contest to secure the European light heavyweight title.
The stadium became quiet for a deeply poignant homage prior to the bout as a bell ceremony sounded in memory of local hero Hatton, who succumbed aged 46 in last month.
It was the premier televised match card in the urban center since Hatton's death. As the last bell disappeared, the stillness became a chant of "there's just one Hatton".
The competition during the bout matched the sentiment. Arthur was sent to the canvas by a significant blow flush on the chin in the second round, standing uncertainly to his feet on the referee's count.
But the Manchester United-red equipment of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was injured quickly, noticeable damage developing under his orbital area as the fighters traded punishing blows.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor edged the result with scoring tallies of 114-114, 115-113 and clearer margin, but each competitor were relentless and brave, exactly what their hero the legend embodied.
