UK light-heavyweight Joshua Buatsi made a winning yet underwhelming start to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a majority decision in a tight ten-round fight at the Co-op Live Arena.
But Parker found success, connecting with powerful single shots in a fight where the approaches failed to mesh, with constant grabbing marring the fight.
The scoring judges judged it 96-94 to Buatsi, with the third a 95-95 draw.
"It wasn't my best display but what defines champions? They prevail," Buatsi commented in the ring as he was greeted with negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to secure a 20th pro success.
Various analysts thought Parker, thirty-one, should have been awarded the victory but the British boxer suffered the second loss of his 28-match career.
Buatsi Earns Victory in Dull Encounter
The fighter's advancement has plateaued in recent years through contract problems and long spells of inactivity.
Earlier forecast as the next star of UK boxing, he now is positioned trying to achieve expectations - maybe in what seems like a ultimate opportunity - under fresh management.
He started carefully, with both competitors willing to overcommit in a tentative initial rounds.
The challenger, whose only previous defeat came at super middleweight against his former opponent in two years ago after suffering a hand injury mid-fight, was participating in his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who utilized a tight guard to barely take the more effective periods.
The crowd's patience decreased during frequent holding, with the challenger going down several times during clinches.
The underdog ended stronger, but several stanzas were challenging to assess. However, ex-champion the boxing analyst - commentating on the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just one round.
Buatsi advances, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - on this evidence - still seems difficult.
Hatton Tribute Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur overcame Rea by close verdict in a terrific Manchester vs Manchester contest to win the continental title.
The stadium fell silent for a extremely emotional homage ahead of the contest as ten bells rang in memory of local hero Hatton, who succumbed 46 years old in last month.
It was the premier televised fight night in the city since Hatton's death. As the last bell faded, the stillness gave way to a roar of "only one Hatton".
The action within the ring equaled the sentiment. The eventual winner was knocked down by a left hook squarely on the jaw in the second round, rising shakily to his feet on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. Across the ring, the opponent - in competitive blue - was damaged quickly, heavy swelling appearing under his face as the pair traded powerful shots.
The challenger, 27, connected with strong blows but Arthur, 34, responded in kind with effective uppercuts as the action rarely dropped over 12 rounds.
The victor barely secured the result with scoring tallies of even score, 115-113 and 115-112, but each competitor were relentless and courageous, exactly what their hero the legend stood for.
