UK light heavyweight Joshua Buatsi secured a victory yet disappointing beginning to life under new promoters with a decision win over Parker in Manchester.
The Olympic medal winner's activity level seemingly secured him a judges' verdict in a close ten-round bout at the boxing arena.
But Parker had his moments, landing some telling individual punches in a contest where the approaches didn't complement each other, with frequent clinching marring the contest.
The scoring judges had it 96-94 for to Buatsi, with the third a even score.
"It wasn't my best performance but what defines champions? They prevail," Buatsi said in the ring as he was met by disapproval from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a 20th career victory.
Some ringside observers believed the challenger, thirty-one, deserved the win but the Derbyshire fighter experienced the second setback of his 28-bout career.
The Champion Earns Win in Slow Affair
Buatsi's progress has stalled in recent times through contract problems and long spells of lack of fights.
Earlier forecast as the rising talent of British boxing, he now is positioned trying to fulfil that early promise - possibly in what feels like a final roll of the dice - under fresh management.
He began cautiously, with the two boxers ready to be aggressive in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand in the contest, was making just his second fight at light heavyweight.
By the middle rounds, the underdog had kept it close, making life awkward for Buatsi, who worked behind a tight guard to narrowly win the cleaner stanzas.
The audience's tolerance wore thin amid regular grabbing, with Parker going down multiple occasions during grappling.
The underdog ended stronger, but many rounds were difficult to score. Although, former world champion Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of power puncher Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels Local Rivalry Fight
In the secondary fight, Arthur beat Rea by split-decision in a terrific all-Manchester battle to capture the European light heavyweight championship.
The arena grew hushed for a deeply poignant homage before the fight as a bell ceremony sounded in remembrance of the city's native Ricky Hatton, who passed away 46 years old in recently.
It was the premier televised match card in the urban center since Hatton's passing. As the final chime disappeared, the quiet transitioned to a roar of "there's just one Hatton".
The competition during the bout matched the feeling. Arthur was sent to the canvas by a powerful punch directly to the jaw in the second round, rising shakily to his footing on the eight count.
But the red-colored shorts of the fighter soon came forward again. From the other corner, the opponent - in rival City blue - was injured early, heavy swelling developing under his eye as the duo exchanged hard punches.
The challenger, 27, landed power punches but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action hardly diminished over the full distance.
The victor edged the decision with scoring tallies of 114-114, close margin and 115-112, but the two athletes were persistent and brave, all the qualities their idol the legend represented.
