UK light-heavyweight Joshua Buatsi made a winning yet underwhelming beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output likely gained him a judges' verdict in a close ten-round fight at the boxing arena.
But the challenger had his moments, landing some telling individual punches in a fight where the techniques never quite clicked, with frequent clinching marring the contest.
Two judges had it 96-94 for to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest showing but what defines champions? They succeed," Buatsi commented in the arena as he was met by negative reactions from the audience.
The British fighter returned to winning ways after his maiden career setback - an epic battle with Callum Smith in last winter - to earn a 20th career victory.
Some ringside observers thought the challenger, thirty-one, should have been awarded the win but the Derbyshire fighter experienced the second setback of his 28-bout career.
The Champion Earns Triumph in Dull Match
Buatsi's progress has slowed in the past few years through contract problems and long spells of lack of fights.
Once tipped as the next star of UK boxing, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under fresh management.
He began cautiously, with both competitors ready to be aggressive in a cagey opening few rounds.
Parker, whose single earlier setback came at super middleweight against his former opponent in 2022 after breaking his hand during the bout, was participating in his second appearance at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who utilized a tight guard to narrowly win the more effective rounds.
The spectators' acceptance decreased during regular grabbing, with Parker going down several times during clinches.
Parker finished the stronger, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - working with the broadcast network - had it particularly wide for Parker, awarding Buatsi just only one stanza.
The victor advances, but with the presence of power puncher David Benavidez, and Eastern European fighter Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Homage Fuels Manchester Derby Contest
In the co-main event, Arthur overcame Bradley Rea by divided decision in a outstanding local rivalry battle to win the European light-heavyweight title.
The stadium grew hushed for a deeply poignant tribute before the fight as 10 bells tolled in honor of Manchester's own Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised match card in the location since the passing of Hatton. As the final chime disappeared, the stillness became a shout of "there's only one Ricky Hatton".
The competition within the ring reflected the sentiment. The eventual winner was knocked down by a powerful punch flush on the chin in the initial stage, getting up unsteadily to his position on the eight count.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in competitive blue - was marked up soon, noticeable damage forming under his face as the pair exchanged hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over twelve rounds.
Arthur edged the verdict with official scores of draw, 115-113 and wider gap, but both fighters were relentless and full of heart, everything their inspiration the legend stood for.
