UK light heavyweight Joshua Buatsi made a winning yet disappointing debut to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight 10-round bout at the Manchester venue.
But Parker found success, delivering effective single shots in a fight where the approaches never quite clicked, with constant grabbing spoiling the contest.
The officials scored it 96-94 for to the winner, with the final judge a even score.
"It wasn't my best performance but what do champions do? They win," Buatsi said in the ring as he was faced boos from the spectators.
The Londoner returned to winning ways after his initial pro loss - an epic battle with his previous opponent in February - to claim a 20th pro success.
Several boxing experts believed the challenger, 31, should have been awarded the decision but the Derbyshire fighter endured the second setback of his 28-fight professional journey.
Buatsi Secures Win in Slow Affair
The fighter's advancement has plateaued in recent times through management issues and long spells of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now is positioned trying to realize his potential - maybe in what appears to be a ultimate opportunity - under recent support.
He started carefully, with both competitors prepared to overcommit in a calculated opening few 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 making just his second fight at the higher weight class.
By the halfway stage, the underdog had made it competitive, causing problems for the favorite, who utilized a tight guard to narrowly win the cleaner periods.
The spectators' acceptance wore thin because of regular grabbing, with Parker slipping to the canvas multiple occasions during close exchanges.
Parker closed well, but multiple periods were hard to judge. Nevertheless, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just a single round.
The victor moves on, but with the presence of heavy hitter Benavidez, and Eastern European fighter Bivol dominating the weight class, the path to championship success - on this evidence - still appears challenging.
Ricky Hatton Memorial Motivates Manchester Derby Fight
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a terrific local rivalry fight to win the continental championship.
The venue became quiet for a deeply poignant tribute ahead of the contest as 10 bells sounded in remembrance of Manchester's own Hatton, who passed away at age 46 in last month.
It was the premier televised fight night in the location since Hatton's death. As the last bell disappeared, the quiet became a shout of "there's only one Ricky Hatton".
The fighting within the ring equaled the sentiment. Arthur was floored by a left hook flush on the jaw in the early round, getting up unsteadily to his position on the eight count.
But the traditional red attire of the fighter soon advanced again. From the other corner, Rea - in competitive blue - was marked up soon, noticeable damage appearing under his orbital area as the duo landed punishing blows.
Rea, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with effective uppercuts as the action seldom decreased over the full distance.
Arthur barely secured the verdict with scoring tallies of draw, close margin and 115-112, but the two athletes were persistent and full of heart, all the qualities their idol Hatton embodied.
