UK light-heavyweight Joshua Buatsi secured a victory yet unimpressive beginning to life under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a tight ten-round contest at the Manchester venue.
But Parker found success, landing some telling single shots in a fight where the techniques failed to mesh, with frequent clinching disrupting the contest.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my finest performance but what defines champions? They win," the victor said in the ringside as he was faced boos from the audience.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in last winter - to claim a 20th career victory.
Some ringside observers believed the challenger, 31, merited the win but the contender endured the second defeat of his 28-fight career.
Buatsi Claims Victory in Uneventful Affair
Buatsi's progress has slowed in recent times through contract problems and extended periods of inactivity.
Earlier forecast as the next star of British boxing, he now finds himself trying to achieve expectations - maybe in what seems like a last chance - under recent support.
He opened tentatively, with both competitors prepared to take risks in a calculated opening few rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after damaging his hand in the contest, was participating in his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for the favorite, who operated with a solid defense to edge the more effective stanzas.
The crowd's patience decreased during regular grabbing, with the challenger slipping to the canvas several times during grappling.
Parker finished the stronger, but many rounds were hard to judge. Although, ex-champion the boxing analyst - working with Dazn - had it particularly wide for Parker, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of power puncher David Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Hatton Tribute Inspires Local Rivalry Battle
In the co-main event, Arthur overcame Bradley Rea by split-decision in a terrific local rivalry fight to capture the continental title.
The venue fell silent for a profoundly moving homage ahead of the contest as 10 bells rang in honor of Manchester's own Hatton, who passed away at age 46 in September.
It was the initial significant broadcast boxing event in the urban center since Hatton's passing. As the concluding sound disappeared, the silence became a roar of "only one Ricky Hatton".
The competition within the ring matched the sentiment. The eventual winner was sent to the canvas by a left hook flush on the chin in the second round, standing uncertainly to his feet on the count of eight.
But the Manchester United-red shorts of Arthur soon came forward again. From the other corner, the opponent - in opposing blue - was injured soon, noticeable damage appearing under his eye as the duo landed hard punches.
Rea, twenty-seven, connected with strong blows but Arthur, 34, matched the intensity with stinging uppercuts as the action rarely dropped over twelve rounds.
The victor narrowly won the result with official scores of 114-114, narrow lead and wider gap, but both fighters were persistent and full of heart, all the qualities their idol the legend represented.
