British light-heavyweight Joshua Buatsi made a winning yet disappointing start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close 10-round fight at the boxing 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 spoiling the fight.
The scoring judges scored it 96-94 to the winner, with the remaining official a 95-95.
"It wasn't my greatest showing but how do champions respond? They succeed," Buatsi said in the arena as he was greeted with disapproval from the audience.
The Londoner returned to winning ways after his maiden career setback - an epic battle with his previous opponent in February - to earn a twentieth professional win.
Various analysts felt Parker, thirty-one, should have been awarded the win but the British boxer experienced the second loss of his 28-bout career.
The Champion Claims Win in Slow Match
His career development has slowed in the past few years through promotional disputes and long spells of inactivity.
Once tipped as the rising talent of the British fight scene, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under new promotional backing.
He opened tentatively, with neither fighter ready to take risks in a tentative early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second bout at light-heavyweight.
By the fight's midpoint, Parker had kept it close, making life awkward for Buatsi, who operated with a solid defense to edge the better rounds.
The spectators' acceptance decreased because of frequent holding, with the challenger going down several times during close exchanges.
The underdog ended stronger, but many rounds were hard to judge. Although, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the caliber of power puncher Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Ricky Hatton Homage Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by split-decision in a excellent all-Manchester fight to capture the European light-heavyweight belt.
The arena grew hushed for a deeply poignant tribute before the fight as a bell ceremony rang in memory of Manchester's own Hatton, who succumbed at age 46 in recently.
It was the first major televised fight night in the city since Hatton's death. As the concluding sound faded, the quiet became a chant of "there's only one Ricky Hatton".
The action during the bout reflected the feeling. The eventual winner was sent to the canvas by a left hook squarely on the face in the initial stage, standing uncertainly to his position on the referee's count.
But the red-colored shorts of the fighter soon pressed ahead again. From the other corner, the opponent - in opposing blue - was damaged early, significant bruising forming under his face as the fighters exchanged punishing blows.
Rea, twenty-seven, landed power punches but the champion, 34, responded in kind with powerful upward punches as the intensity hardly diminished over twelve rounds.
The victor narrowly won the result with scoring tallies of draw, close margin and 115-112, but the two athletes were determined and full of heart, all the qualities their idol Hatton represented.
