British light-heavyweight Joshua Buatsi secured a victory yet disappointing start to life under fresh promotional backing with a points victory over Parker in Manchester.
The Olympic bronze medallist's work rate likely gained him a judges' verdict in a competitive ten-round contest at the Co-op Live Arena.
But Parker had his moments, connecting with powerful clean blows in a fight where the approaches failed to mesh, with excessive holding disrupting the contest.
The scoring judges scored it 96-94 for to the winner, with the third a 95-95 draw.
"It wasn't my finest showing but what defines champions? They win," Buatsi said in the ring as he was faced disapproval from the audience.
The Londoner got back to winning after his initial pro loss - an thrilling contest with his previous opponent in February - to earn a 20th career victory.
Some ringside observers felt Parker, thirty-one, should have been awarded the decision but the contender endured the second loss of his 28-fight professional journey.
The Champion Secures Win in Dull Affair
Buatsi's progress has stalled in recent years through contract problems and considerable time of inactivity.
Earlier forecast as the rising talent of the British fight scene, he now finds himself trying to realize his potential - perhaps in what appears to be a final roll of the dice - under fresh management.
He started carefully, with both competitors prepared to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against John Ryder in two years ago after breaking his hand during the bout, was competing in only his second appearance at light heavyweight.
By the middle rounds, the underdog had kept it close, creating difficulties for Buatsi, who operated with a tight guard to barely take the better periods.
The crowd's patience diminished because of regular grabbing, with Parker slipping to the canvas several times during close exchanges.
The underdog ended stronger, but several stanzas were challenging to assess. Nevertheless, former world champion Carl Frampton - commentating on the broadcast network - had it strongly leaning for Parker, scoring for Buatsi just one round.
Buatsi progresses, but with the caliber of heavy hitter Benavidez, and Eastern European fighter Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Tribute Inspires Manchester Derby Fight
In the secondary fight, Lyndon Arthur beat Bradley Rea by close verdict in a terrific local rivalry battle to capture the continental championship.
The arena fell silent for a profoundly moving memorial prior to the bout as a bell ceremony sounded in remembrance of local hero Hatton, who succumbed aged 46 in September.
It was the first major televised fight night in the city since Hatton's passing. As the last bell faded, the stillness gave way to a chant of "there's only one Hatton".
The competition inside the ropes reflected the feeling. Arthur was floored by a significant blow squarely on the jaw in the second round, standing uncertainly to his position on the count of eight.
But the traditional red attire of the fighter soon pressed ahead again. Across the ring, Rea - in opposing blue - was marked up soon, significant bruising forming under his face as the pair traded punishing blows.
Rea, 27, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the intensity seldom decreased over the full distance.
The victor narrowly won the decision with scoring tallies of 114-114, 115-113 and wider gap, but the two athletes were persistent and full of heart, everything their inspiration the legend embodied.
