UK light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate seemingly secured him a majority decision in a tight ten-round bout at the Manchester venue.
But Parker landed significant shots, delivering effective single shots in a match where the styles didn't complement each other, with excessive holding marring the action.
The scoring judges judged it 96-94 for to Buatsi, with the remaining official a even score.
"It wasn't my greatest performance but what do champions do? They win," Buatsi stated in the ringside as he was met by boos from the audience.
The British fighter bounced back after his maiden career setback - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-fight career.
Buatsi Claims Win in Dull Encounter
His career development has slowed in recent times through promotional disputes and considerable time of inactivity.
Earlier forecast as the rising talent of UK boxing, he now is positioned trying to realize his potential - perhaps in what seems like a ultimate opportunity - under new promotional backing.
He opened tentatively, with the two boxers willing to be aggressive in a tentative early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was participating in his second fight at the higher weight class.
By the halfway stage, the underdog had kept it close, making life awkward for the favorite, who operated with a tight guard to narrowly win the better rounds.
The spectators' acceptance decreased during constant clinching, with Parker falling to the floor various instances during close exchanges.
Parker ended stronger, but several stanzas were difficult to score. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it particularly wide for Parker, giving Buatsi just only one stanza.
The victor progresses, but with the likes of hard hitter Benavidez, and Eastern European fighter Dmitry Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Contest
In the co-main event, Arthur beat Bradley Rea by split-decision in a outstanding local rivalry contest to win the European light-heavyweight championship.
The venue became quiet for a profoundly moving memorial prior to the bout as a bell ceremony rang in honor of local hero Hatton, who succumbed aged 46 in recently.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the concluding sound ended, the silence gave way to a chant of "there's only one Hatton".
The competition inside the ropes reflected the feeling. Arthur was sent to the canvas by a left hook flush on the chin in the second round, rising shakily to his position on the referee's count.
But the traditional red equipment of Arthur soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up early, significant bruising forming under his eye as the fighters landed punishing blows.
Rea, twenty-seven, delivered effective strikes but Arthur, thirty-four, responded in kind with effective uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the result with scoring tallies of even score, narrow lead and clearer margin, but each competitor were relentless and courageous, everything their inspiration the legend embodied.
