UK light-heavyweight Joshua Buatsi secured a victory yet disappointing debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a majority decision in a close 10-round bout at the Manchester venue.
But Parker found success, connecting with powerful individual punches in a contest where the styles never quite clicked, with frequent clinching disrupting the fight.
The scoring judges had it 96-94 for to Buatsi, with the third a 95-95.
"It wasn't my best performance but what defines champions? They prevail," Buatsi stated in the ringside as he was greeted with disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with Callum Smith in February - to earn a 20th pro success.
Several boxing experts believed the challenger, 31, should have been awarded the victory but the Derbyshire fighter experienced the second loss of his 28-bout career.
The Champion Secures Triumph in Dull Match
The fighter's advancement has slowed in the past few years through management issues and long spells of lack of fights.
Once tipped as the rising talent of UK boxing, he now finds himself trying to realize his potential - maybe in what appears to be a last chance - under recent support.
He began cautiously, with the two boxers willing to take risks in a cagey initial rounds.
The challenger, whose single earlier setback came at the lower weight class against John Ryder in two years ago after suffering a hand injury during the bout, was making just his second bout at light heavyweight.
By the halfway stage, Parker had stayed in contention, causing problems for Buatsi, who worked behind a tight guard to barely take the more effective stanzas.
The audience's tolerance decreased amid constant clinching, with the challenger slipping to the canvas various instances during clinches.
Parker ended stronger, but many rounds were difficult to score. Although, former world champion the boxing analyst - working with the broadcast network - had it significantly in favor for the challenger, giving Buatsi just a single round.
Buatsi progresses, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Fuels All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a outstanding all-Manchester contest to capture the European light heavyweight championship.
The stadium fell silent for a profoundly moving memorial ahead of the contest as a bell ceremony rang in remembrance of Manchester's own Hatton, who succumbed 46 years old in recently.
It was the first major televised match card in the location since Hatton's death. As the final chime faded, the quiet became a roar of "only one Hatton".
The fighting inside the ropes equaled the emotion. The eventual winner was floored by a left hook flush on the face in the early round, getting up unsteadily to his feet on the count of eight.
But the traditional red shorts of the fighter soon advanced again. On the opposite side, Rea - in competitive blue - was marked up early, heavy swelling developing under his eye as the pair landed powerful shots.
The challenger, 27, delivered effective strikes but the champion, 34, matched the intensity with stinging uppercuts as the action seldom decreased over the full distance.
Arthur barely secured the result with scoring tallies of draw, close margin and 115-112, but the two athletes were persistent and courageous, everything their hero the legend represented.
