UK light heavyweight Joshua Buatsi made a winning yet disappointing start to life under recent management with a unanimous decision over Parker in the Manchester arena.
The Olympic bronze medallist's activity level likely gained him a majority decision in a close ten-round bout at the Manchester venue.
But Parker found success, landing some telling individual punches in a match where the approaches didn't complement each other, with constant grabbing marring the fight.
Two judges judged it 96-94 to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but how do champions respond? They prevail," the victor stated in the ringside as he was greeted with boos from the spectators.
The British fighter bounced back after his maiden career setback - an thrilling contest with Callum Smith in February - to claim a 20th career victory.
Some ringside observers felt the challenger, 31, merited the win but the contender experienced the second setback of his 28-bout professional journey.
Buatsi's progress has plateaued in recent years through management issues and extended periods of lack of fights.
Previously predicted as the next star of British boxing, he now is positioned trying to realize his potential - perhaps in what feels like a last chance - under recent support.
He opened tentatively, with neither fighter ready to overcommit in a cagey early stages.
Parker, whose only previous defeat came at the lower weight class against John Ryder in two years ago after breaking his hand during the bout, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the cleaner rounds.
The spectators' acceptance wore thin during frequent holding, with the challenger falling to the floor several times during grappling.
Parker finished the stronger, but many rounds were hard to judge. However, ex-champion the boxing analyst - commentating on the broadcast network - had it particularly wide for the challenger, giving Buatsi just only one stanza.
Buatsi advances, but with the likes of heavy hitter Benavidez, and Russian champion Bivol dominating the weight class, the path to championship success - on this evidence - still seems difficult.
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a excellent local rivalry battle to secure the continental title.
The arena became quiet for a deeply poignant memorial before the fight as 10 bells rang in remembrance of Manchester's own Hatton, who succumbed 46 years old in last month.
It was the initial significant broadcast boxing event in the city since the passing of Hatton. As the final chime faded, the quiet transitioned to a roar of "there's just one Hatton".
The competition within the ring matched the sentiment. Arthur was knocked down by a significant blow squarely on the chin in the second round, rising shakily to his position on the count of eight.
But the red-colored shorts of Arthur soon pressed ahead again. Across the ring, the opponent - in opposing blue - was marked up soon, significant bruising forming under his orbital area as the pair exchanged hard punches.
The challenger, 27, landed power punches but Arthur, 34, responded in kind with effective uppercuts as the intensity rarely dropped over twelve rounds.
Arthur narrowly won the decision with official scores of draw, close margin and clearer margin, but each competitor were determined and courageous, everything their idol the legend embodied.