British light-heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's work rate likely gained him a majority decision in a close ten-round fight at the Co-op Live Arena.
But the challenger had his moments, connecting with powerful individual punches in a match where the techniques never quite clicked, with excessive holding marring the contest.
The scoring judges had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest performance but what defines champions? They succeed," the victor commented in the arena as he was greeted with boos from the crowd.
The Londoner got back to winning after his initial pro loss - an thrilling contest with Callum Smith in last winter - to claim a 20th career victory.
Several boxing experts believed Parker, thirty-one, deserved the victory but the contender suffered the second setback of his 28-fight career.
The Champion Earns Win in Slow Affair
His career development has stalled in recent years through promotional disputes and long spells of inactivity.
Once tipped as the next star of UK boxing, he now finds himself trying to realize his potential - perhaps in what seems like a last chance - under new promotional backing.
He began cautiously, with neither fighter prepared to take risks in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against John Ryder in two years ago after suffering a hand injury mid-fight, was making just his second bout at light heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who utilized a protective stance to narrowly win the more effective rounds.
The spectators' acceptance diminished amid frequent holding, with Parker slipping to the canvas multiple occasions during clinches.
Parker ended stronger, but several stanzas were hard to judge. However, previous titleholder Carl Frampton - providing analysis for Dazn - had it strongly leaning for Parker, giving Buatsi just one round.
Buatsi progresses, but with the likes of heavy hitter Benavidez, and Russian star Bivol leading the category, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Inspires Manchester Derby Battle
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a terrific local rivalry fight to capture the European light heavyweight championship.
The arena became quiet for a deeply poignant homage prior to the bout as a bell ceremony sounded in remembrance of the city's native Hatton, who succumbed at age 46 in last month.
It was the premier televised match card in the city since Hatton's passing. As the last bell ended, the quiet transitioned to a roar of "there's only one Hatton".
The action inside the ropes equaled the sentiment. Arthur was knocked down by a left hook squarely on the jaw in the initial stage, getting up unsteadily to his footing on the count of eight.
But the red-colored attire of Arthur soon pressed ahead again. Across the ring, Rea - in competitive blue - was marked up soon, heavy swelling appearing under his face as the pair traded hard punches.
The challenger, twenty-seven, landed power punches but the champion, thirty-four, matched the intensity with stinging uppercuts as the intensity seldom decreased over 12 rounds.
The victor narrowly won the result with scoring tallies of 114-114, close margin and clearer margin, but each competitor were relentless and full of heart, all the qualities their hero Hatton embodied.
