British light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic medal winner's work rate appeared to earn him a majority decision in a close 10-round fight at the Co-op Live Arena.
But Parker landed significant shots, connecting with powerful individual punches in a contest where the approaches failed to mesh, with frequent clinching marring the fight.
The officials judged it 96-94 in favor to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but how do champions respond? They win," Buatsi stated in the ring as he was greeted with negative reactions from the spectators.
The Londoner bounced back after his initial pro loss - an epic battle with his previous opponent in last winter - to secure a 20th career victory.
Some ringside observers thought the challenger, 31, merited the victory but the British boxer suffered the second setback of his 28-match career.
Buatsi Earns Triumph in Slow Match
The fighter's advancement has slowed in recent times through contract problems and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now stands trying to realize his potential - perhaps in what feels like a last chance - under recent support.
He began cautiously, with both competitors willing to take risks in a tentative initial rounds.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury during the bout, was participating in his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for the favorite, who utilized a solid defense to barely take the cleaner rounds.
The spectators' acceptance decreased during regular grabbing, with the challenger going down several times during close exchanges.
The underdog finished the stronger, but multiple periods were difficult to score. However, previous titleholder the boxing analyst - working with the broadcast network - had it significantly in favor for Parker, awarding Buatsi just one round.
Buatsi progresses, but with the caliber of hard hitter Benavidez, and Russian star Bivol dominating the weight class, the journey to titles - judging by this showing - still seems difficult.
Ricky Hatton Memorial Fuels Manchester Derby Battle
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a terrific Manchester vs Manchester contest to win the European light heavyweight belt.
The arena fell silent for a deeply poignant tribute ahead of the contest as a bell ceremony tolled in remembrance of local hero Hatton, who died 46 years old in last month.
It was the premier televised match card in the location since Hatton's death. As the final chime disappeared, the quiet gave way to a chant of "there's just one Hatton".
The fighting inside the ropes matched the emotion. The eventual winner was knocked down by a left hook directly to the chin in the second round, standing uncertainly 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 competitive blue - was marked up early, heavy swelling forming under his orbital area as the fighters traded powerful shots.
The challenger, 27, landed power punches but Arthur, 34, responded in kind with powerful upward punches as the intensity seldom decreased over twelve rounds.
Arthur edged the verdict with official scores of 114-114, 115-113 and wider gap, but each competitor were determined and courageous, everything their inspiration the legend represented.
