UK light heavyweight Joshua Buatsi made a winning yet unimpressive debut to life under fresh promotional backing with a points victory over Parker in the Manchester arena.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive ten-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful individual punches in a contest where the approaches failed to mesh, with frequent clinching spoiling the fight.
The scoring judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my greatest display but what defines champions? They prevail," Buatsi commented in the ring as he was greeted with negative reactions from the spectators.
The British fighter returned to winning ways after his initial pro loss - an epic battle with Callum Smith in February - to claim a 20th pro success.
Some ringside observers felt the challenger, thirty-one, merited the victory but the British boxer endured the second loss of his 28-match professional journey.
The Champion Secures Win in Uneventful Match
The fighter's advancement has slowed in recent years through management issues and long spells of lack of fights.
Once tipped as the next star of UK boxing, he now is positioned trying to fulfil that early promise - possibly in what appears to be a last chance - under fresh management.
He began cautiously, with neither fighter willing to take risks in a tentative early stages.
The challenger, whose single earlier setback came at super middleweight against John Ryder in 2022 after suffering a hand injury mid-fight, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had stayed in contention, creating difficulties for Buatsi, who worked behind a tight guard to barely take the better rounds.
The audience's tolerance decreased during constant clinching, with Parker slipping to the canvas several times during clinches.
The underdog closed well, but several stanzas were difficult to score. However, former world champion the boxing analyst - working with Dazn - had it significantly in favor for the challenger, giving Buatsi just a single round.
The victor progresses, but with the caliber of power puncher Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still appears challenging.
Hatton Tribute Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester contest to secure the continental title.
The stadium became quiet for a deeply poignant tribute before the fight as 10 bells tolled in remembrance of local hero Hatton, who died aged 46 in September.
It was the first major televised match card in the urban center since Hatton's death. As the final chime faded, the stillness gave way to a shout of "only one Hatton".
The competition within the ring reflected the emotion. The eventual winner was sent to the canvas by a left hook squarely on the jaw in the second round, standing uncertainly to his position on the count of eight.
But the red-colored equipment of Arthur soon pressed ahead again. From the other corner, Rea - in opposing blue - was damaged soon, significant bruising developing under his eye as the duo landed hard punches.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over twelve rounds.
The victor narrowly won the verdict with official scores of draw, close margin and clearer margin, but each competitor were persistent and full of heart, everything their inspiration the legend embodied.
