UK light heavyweight Joshua Buatsi made a winning yet disappointing start to life under new promoters with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a judges' verdict in a competitive ten-round fight at the boxing arena.
But Parker had his moments, landing some telling individual punches in a contest where the styles didn't complement each other, with excessive holding disrupting the fight.
The officials judged it 96-94 to Buatsi, with the final judge a 95-95 draw.
"It wasn't my greatest performance but what do champions do? They prevail," Buatsi said in the ring as he was greeted with disapproval from the crowd.
The British fighter got back to winning after his first professional defeat - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts felt the challenger, 31, should have been awarded the victory but the British boxer experienced the second loss of his 28-bout professional journey.
The Champion Earns Victory in Dull Match
Buatsi's progress has slowed in the past few years through management issues and considerable time of inactivity.
Previously predicted as the future of the British fight scene, he now is positioned trying to achieve expectations - perhaps in what feels like a last chance - under fresh management.
He opened tentatively, with neither fighter ready to be aggressive in a calculated early stages.
The challenger, whose only previous defeat came at the lower weight class against his former opponent in two years ago after suffering a hand injury during the bout, was competing in only his second fight at light heavyweight.
By the halfway stage, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to barely take the better rounds.
The spectators' acceptance decreased during frequent holding, with the challenger slipping to the canvas several times during grappling.
Parker finished the stronger, but several stanzas were difficult to score. Nevertheless, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just only one stanza.
Buatsi advances, but with the presence of heavy hitter Benavidez, and Russian champion Dmitry Bivol leading the category, the road to world glory - on this evidence - still looks steep.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the supporting bout, Lyndon Arthur beat Rea by divided decision in a terrific all-Manchester battle to capture the European light heavyweight championship.
The venue became quiet for a extremely emotional memorial ahead of the contest as a bell ceremony sounded in memory of the city's native Ricky Hatton, who died at age 46 in September.
It was the first major televised match card in the location since the passing of Hatton. As the last bell disappeared, the quiet became a shout of "only one Hatton".
The fighting within the ring equaled the emotion. The eventual winner was knocked down by a significant blow directly to the chin in the initial stage, standing uncertainly to his feet on the eight count.
But the traditional red equipment of Arthur soon pressed ahead again. Across the ring, Rea - in rival City blue - was damaged quickly, noticeable damage developing under his face as the duo traded punishing blows.
The challenger, 27, connected with strong blows but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity rarely dropped over the full distance.
Arthur narrowly won the decision with scoring tallies of 114-114, 115-113 and clearer margin, but the two athletes were persistent and courageous, everything their hero Hatton represented.
