UK light heavyweight Joshua Buatsi made a winning yet unimpressive start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a competitive ten-round bout at the Co-op Live Arena.
But Parker landed significant shots, delivering effective single shots in a contest where the styles never quite clicked, with constant grabbing marring the fight.
The scoring judges had it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my best showing but what do champions do? They prevail," the victor said in the ring as he was met by disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the Derbyshire fighter experienced the second defeat of his 28-fight career.
The Champion Earns Triumph in Slow Match
His career development has slowed in the past few years through contract problems and considerable time of inactivity.
Once tipped as the future of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with both competitors prepared to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at super-middleweight against his former opponent in two years ago after suffering a hand injury in the contest, was competing in only his second fight at light-heavyweight.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to narrowly win the cleaner stanzas.
The audience's tolerance decreased because of frequent holding, with Parker going down several times during close exchanges.
The underdog closed well, but many rounds were challenging to assess. Although, former world champion the boxing analyst - providing analysis for Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Homage Inspires All-Manchester Fight
In the co-main event, Lyndon Arthur defeated Rea by split-decision in a outstanding all-Manchester fight to secure the continental belt.
The venue grew hushed for a deeply poignant tribute before the fight as ten bells rang in honor of the city's native Hatton, who passed away 46 years old in last month.
It was the premier televised match card in the urban center since the passing of Hatton. As the final chime disappeared, the quiet transitioned to a chant of "there's only one Hatton".
The fighting within the ring reflected the sentiment. Arthur was knocked down by a left hook flush on the jaw in the second round, rising shakily to his position on the referee's count.
But the red-colored shorts of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was damaged soon, significant bruising appearing under his orbital area as the duo traded hard punches.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the result with official scores of 114-114, narrow lead and 115-112, but each competitor were relentless and courageous, exactly what their inspiration Hatton represented.
