British light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a split decision in a close 10-round bout at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful individual punches in a fight where the approaches never quite clicked, with excessive holding spoiling the fight.
Two judges had it 96-94 for to the winner, with the final judge a even score.
"It wasn't my greatest performance but what defines champions? They prevail," the victor stated in the ring as he was faced disapproval from the spectators.
The British fighter got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to secure a 20th pro success.
Some ringside observers thought the challenger, 31, deserved the victory but the contender experienced the second defeat of his 28-bout career.
The Champion Secures Triumph in Uneventful Match
Buatsi's progress has plateaued in the past few years through management issues and long spells of inactivity.
Once tipped as the next star of British boxing, he now finds himself trying to achieve expectations - possibly in what seems like a ultimate opportunity - under recent support.
He started carefully, with the two boxers ready to be aggressive in a calculated initial rounds.
The challenger, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand mid-fight, was participating in his second bout at light-heavyweight.
By the middle rounds, the underdog had made it competitive, causing problems for Buatsi, who operated with a protective stance to barely take the more effective periods.
The audience's tolerance wore thin because of constant clinching, with the challenger slipping to the canvas several times during close exchanges.
Parker ended stronger, but several stanzas were difficult to score. However, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, awarding Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian star Dmitry Bivol leading the category, the journey to titles - on this evidence - still appears challenging.
Ricky Hatton Homage Motivates All-Manchester Contest
In the secondary fight, Lyndon Arthur defeated Bradley Rea by split-decision in a excellent local rivalry battle to secure the European light-heavyweight title.
The venue grew hushed for a deeply poignant memorial before the fight as a bell ceremony tolled in honor of Manchester's own Hatton, who succumbed at age 46 in September.
It was the premier televised match card in the city since Hatton's death. As the last bell faded, the quiet gave way to a shout of "only one Hatton".
The action during the bout reflected the feeling. The eventual winner was knocked down by a left hook squarely on the face in the second round, rising shakily to his footing on the eight count.
But the Manchester United-red equipment of Arthur soon pressed ahead again. From the other corner, the opponent - in competitive blue - was marked up soon, heavy swelling forming under his orbital area as the fighters traded hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with powerful upward punches as the pace hardly diminished over the full distance.
The victor edged the decision with judges scorecards of even score, 115-113 and 115-112, but the two athletes were determined and courageous, exactly what their inspiration the legend stood for.
