UK light heavyweight Joshua Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic bronze medallist's work rate seemingly secured him a split decision in a competitive 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, landing some telling single shots in a match where the approaches didn't complement each other, with excessive holding disrupting the contest.
Two judges scored it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my greatest display but how do champions respond? They win," the victor stated in the ringside as he was greeted with disapproval from the spectators.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a twentieth professional win.
Some ringside observers felt Parker, 31, should have been awarded the decision but the Derbyshire fighter endured the second loss of his 28-fight professional journey.
Buatsi Earns Victory in Dull Match
His career development has slowed in the past few years through contract problems and considerable time of lack of fights.
Previously predicted as the future of the British fight scene, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under recent support.
He opened tentatively, with both competitors willing to overcommit in a tentative opening few rounds.
The challenger, whose sole prior loss came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was competing in only his second appearance at the higher weight class.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who utilized a tight guard to barely take the better rounds.
The crowd's patience diminished because of constant clinching, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but several stanzas were hard to judge. Nevertheless, ex-champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the likes of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still looks steep.
Hatton Tribute Fuels Local Rivalry Contest
In the co-main event, Lyndon Arthur defeated Rea by divided decision in a excellent local rivalry battle to win the European light heavyweight belt.
The venue grew hushed for a profoundly moving memorial prior to the bout as ten bells tolled in memory of the city's native Ricky Hatton, who died at age 46 in last month.
It was the initial significant broadcast boxing event in the location since Hatton's passing. As the final chime disappeared, the silence gave way to a shout of "there's just one Ricky Hatton".
The action during the bout reflected the emotion. The eventual winner was knocked down by a left hook squarely on the chin in the second round, rising shakily to his position on the referee's count.
But the red-colored attire of Arthur soon came forward again. On the opposite side, Rea - in opposing blue - was damaged quickly, noticeable damage developing under his face as the duo exchanged hard punches.
The challenger, twenty-seven, delivered effective strikes but the champion, thirty-four, matched the intensity with powerful upward punches as the intensity hardly diminished over twelve rounds.
Arthur narrowly won the verdict with scoring tallies of 114-114, narrow lead and 115-112, but the two athletes were determined and full of heart, all the qualities their inspiration the legend embodied.
