British light-heavyweight Joshua Buatsi made a winning yet underwhelming debut to life under fresh promotional backing with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output likely gained him a split decision in a competitive ten-round contest at the boxing arena.
But the challenger found success, connecting with powerful clean blows in a match where the approaches didn't complement each other, with excessive holding marring the fight.
Two judges had it 96-94 for to the winner, with the final judge a 95-95.
"It wasn't my best display but how do champions respond? They prevail," Buatsi stated in the ringside as he was met by negative reactions from the audience.
The British fighter got back to winning after his initial pro loss - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts felt the challenger, 31, deserved the win but the contender suffered the second loss of his 28-match professional journey.
The Champion Claims Victory in Uneventful Match
Buatsi's progress has stalled in recent years through management issues and considerable time of inactivity.
Previously predicted as the rising talent of UK boxing, he now stands trying to achieve expectations - perhaps in what seems like a final roll of the dice - under fresh management.
He began cautiously, with both competitors ready to be aggressive in a cagey initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was making just his second fight at the higher weight class.
By the fight's midpoint, Parker had kept it close, creating difficulties for the favorite, who utilized a solid defense to narrowly win the more effective periods.
The crowd's patience diminished during constant clinching, with Parker slipping to the canvas several times during clinches.
The underdog finished the stronger, but many rounds were hard to judge. However, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the caliber of heavy hitter Benavidez, and Russian star Bivol leading the category, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Homage Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by divided decision in a terrific Manchester vs Manchester fight to capture the European light heavyweight belt.
The stadium fell silent for a profoundly moving memorial ahead of the contest as a bell ceremony rang in memory of the city's native Ricky Hatton, who died 46 years old in recently.
It was the first major televised boxing event in the city since Hatton's passing. As the last bell disappeared, the silence gave way to a roar of "only one Ricky Hatton".
The competition during the bout reflected the emotion. The eventual winner was knocked down by a powerful punch flush on the chin in the early round, getting up unsteadily to his position on the count of eight.
But the red-colored shorts of the fighter soon pressed ahead again. Across the ring, the opponent - in opposing blue - was injured quickly, significant bruising appearing under his eye as the duo exchanged hard punches.
Rea, 27, connected with strong blows but Arthur, thirty-four, fought fire with fire with stinging uppercuts as the pace seldom decreased over 12 rounds.
The victor narrowly won the decision with judges scorecards of even score, narrow lead and wider gap, but each competitor were relentless and courageous, everything their idol Hatton stood for.
