UK light heavyweight Joshua Buatsi earned a win yet underwhelming start to life under recent management with a points victory over Parker in Manchester.
The Olympic medal winner's punch output seemingly secured him a split decision in a tight ten-round contest at the Co-op Live Arena.
But Parker landed significant shots, landing some telling single shots in a contest where the techniques failed to mesh, with excessive holding spoiling the fight.
The scoring judges judged it 96-94 for to the winner, with the third a 95-95.
"It wasn't my greatest performance but what defines champions? They succeed," Buatsi stated in the ringside as he was greeted with disapproval from the spectators.
The Londoner returned to winning ways after his first professional defeat - an thrilling contest with Callum Smith in last winter - to claim a 20th pro success.
Some ringside observers felt the challenger, 31, should have been awarded the decision but the contender suffered the second loss of his 28-match career.
The Champion Claims Victory in Slow Affair
The fighter's advancement has plateaued in recent years through management issues and considerable time of lack of fights.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to realize his potential - maybe in what appears to be a ultimate opportunity - under recent support.
He began cautiously, with both competitors willing to be aggressive in a tentative initial rounds.
Parker, whose only previous defeat came at the lower weight class against his former opponent in two years ago after damaging his hand in the contest, was making just his second bout at the higher weight class.
By the middle rounds, the underdog had made it competitive, causing problems for the favorite, who operated with a solid defense to edge the more effective rounds.
The crowd's patience wore thin during frequent holding, with the challenger falling to the floor multiple occasions during grappling.
Parker ended stronger, but many rounds were challenging to assess. However, ex-champion Carl Frampton - providing analysis for the broadcast network - had it particularly wide for the challenger, scoring for Buatsi just a single round.
Buatsi moves on, but with the presence of hard hitter Benavidez, and Eastern European fighter Bivol ruling the division, the journey to titles - based on this performance - still appears challenging.
Ricky Hatton Homage Motivates Manchester Derby Battle
In the secondary fight, Arthur defeated Rea by close verdict in a outstanding all-Manchester battle to capture the European light heavyweight title.
The arena became quiet for a extremely emotional homage before the fight as ten bells tolled in remembrance of the city's native Hatton, who succumbed at age 46 in last month.
It was the initial significant broadcast fight night in the location since Hatton's death. As the last bell faded, the stillness became a chant of "only one Hatton".
The competition within the ring reflected the emotion. Arthur was floored by a significant blow flush on the chin in the early round, standing uncertainly to his footing on the count of eight.
But the red-colored shorts of the fighter soon advanced again. Across the ring, Rea - in rival City blue - was damaged quickly, significant bruising forming under his face as the fighters exchanged powerful shots.
Rea, twenty-seven, delivered effective strikes but Arthur, 34, responded in kind with effective uppercuts as the intensity hardly diminished over 12 rounds.
The victor barely secured the verdict with judges scorecards of 114-114, close margin and clearer margin, but the two athletes were determined and courageous, everything their hero the legend stood for.
