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 medal winner's activity level appeared to earn him a judges' verdict in a competitive 10-round fight at the boxing arena.
But Parker landed significant shots, landing some telling clean blows in a contest where the styles failed to mesh, with excessive holding spoiling the action.
The scoring judges had it 96-94 for to Buatsi, with the final judge a even score.
"It wasn't my best display but what defines champions? They win," the victor stated in the ringside as he was met by negative reactions from the crowd.
The British fighter bounced back after his first professional defeat - an thrilling contest with his previous opponent in February - to earn a 20th pro success.
Some ringside observers felt Parker, thirty-one, deserved the victory but the British boxer endured the second setback of his 28-fight professional journey.
Buatsi Claims Triumph in Uneventful Encounter
His career development has stalled in the past few years through contract problems and long spells of inactivity.
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 ultimate opportunity - under fresh management.
He started carefully, with both competitors prepared to be aggressive in a cagey opening few rounds.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand mid-fight, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had made it competitive, creating difficulties for the favorite, who utilized a tight guard to edge the more effective periods.
The audience's tolerance diminished during regular grabbing, with Parker going down multiple occasions during grappling.
Parker ended stronger, but several stanzas were hard to judge. Although, former world champion the boxing analyst - commentating on the broadcast network - had it strongly leaning for Parker, giving Buatsi just a single round.
Buatsi advances, 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 looks steep.
Hatton Homage Fuels Manchester Derby Fight
In the supporting bout, Lyndon Arthur overcame Rea by split-decision in a outstanding local rivalry contest to secure the European light-heavyweight championship.
The arena became quiet for a extremely emotional tribute before the fight as a bell ceremony rang in memory of local hero Hatton, who succumbed 46 years old in last month.
It was the first major televised match card in the city since Hatton's death. As the last bell disappeared, the silence gave way to a shout of "there's only one Hatton".
The fighting during the bout reflected the sentiment. Arthur was sent to the canvas by a left hook directly to the face in the early round, standing uncertainly to his position on the count of eight.
But the traditional red attire of the fighter soon came forward again. On the opposite side, Rea - in rival City blue - was damaged soon, significant bruising forming under his face as the fighters exchanged powerful shots.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, fought fire with fire with powerful upward punches as the action rarely dropped over 12 rounds.
The victor edged the result with scoring tallies of 114-114, 115-113 and 115-112, but each competitor were relentless and courageous, everything their inspiration the legend represented.
