UK light heavyweight Joshua Buatsi secured a victory yet unimpressive debut to life under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's punch output seemingly secured him a split decision in a tight ten-round bout at the boxing arena.
But Parker landed significant shots, landing some telling individual punches in a contest where the techniques never quite clicked, with excessive holding marring the action.
The officials judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest display but how do champions respond? They succeed," Buatsi stated in the ring as he was greeted with boos from the audience.
The British fighter returned to winning ways after his maiden career setback - an memorable fight with his previous opponent in February - to earn a 20th career victory.
Various analysts thought Parker, thirty-one, deserved the victory but the British boxer experienced the second setback of his 28-fight career.
Buatsi Claims Win in Slow Match
His career development has stalled in recent years through promotional disputes and long spells of lack of fights.
Once tipped as the next star of UK boxing, he now stands trying to achieve expectations - perhaps in what seems like a final roll of the dice - under fresh management.
He began cautiously, with the two boxers prepared to take risks in a cagey opening few rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in 2022 after breaking his hand mid-fight, was making just his second appearance at light-heavyweight.
By the halfway stage, Parker had made it competitive, causing problems for Buatsi, who utilized a solid defense to edge the better stanzas.
The audience's tolerance wore thin during frequent holding, with Parker falling to the floor several times during clinches.
The underdog finished the stronger, but several stanzas were difficult to score. However, previous titleholder the boxing analyst - working with Dazn - had it strongly leaning for the challenger, scoring for Buatsi just one round.
Buatsi moves on, but with the caliber of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - judging by this showing - still appears challenging.
Hatton Memorial Fuels Manchester Derby Contest
In the secondary fight, Arthur beat Rea by split-decision in a outstanding Manchester vs Manchester fight to win the European light-heavyweight title.
The arena fell silent for a profoundly moving tribute ahead of the contest as ten bells rang in remembrance of local hero Hatton, who passed away aged 46 in September.
It was the initial significant broadcast match card in the city since Hatton's death. As the final chime ended, the stillness became a chant of "there's just one Ricky Hatton".
The fighting during the bout equaled the sentiment. The eventual winner was sent to the canvas by a significant blow squarely on the jaw in the initial stage, getting up unsteadily to his feet on the referee's count.
But the Manchester United-red shorts of Arthur soon pressed ahead again. From the other corner, Rea - in rival City blue - was marked up early, heavy swelling appearing under his orbital area as the pair exchanged hard punches.
Rea, 27, landed power punches but the champion, thirty-four, matched the intensity with effective uppercuts as the pace rarely dropped over 12 rounds.
The victor narrowly won the decision with judges scorecards of 114-114, 115-113 and clearer margin, but each competitor were determined and courageous, exactly what their hero the legend stood for.
