UK light heavyweight Joshua Buatsi made a winning yet disappointing beginning to life under recent management with a decision win over Parker in Manchester.
The Olympic medal winner's work rate seemingly secured him a split decision in a close 10-round bout at the Co-op Live Arena.
But Parker found success, landing some telling single shots in a match where the techniques never quite clicked, with frequent clinching marring the fight.
Two judges had it 96-94 in favor to Buatsi, with the final judge a 95-95 draw.
"It wasn't my finest display but what defines champions? They prevail," Buatsi said in the arena as he was greeted with disapproval from the audience.
The Londoner got back to winning after his first professional defeat - an memorable fight with his previous opponent in last winter - to claim a 20th pro success.
Several boxing experts felt the challenger, 31, deserved the decision but the Derbyshire fighter suffered the second setback of his 28-match professional journey.
The Champion Claims Triumph in Uneventful Affair
Buatsi's progress has slowed in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the future of British boxing, he now finds himself trying to fulfil that early promise - possibly in what feels like a ultimate opportunity - under recent support.
He started carefully, with both competitors prepared to overcommit in a cagey opening few rounds.
The challenger, whose sole prior loss came at super middleweight against his former opponent in 2022 after suffering a hand injury mid-fight, was participating in his second appearance at light heavyweight.
By the middle rounds, Parker had stayed in contention, causing problems for the favorite, who worked behind a protective stance to narrowly win the more effective stanzas.
The spectators' acceptance wore thin amid frequent holding, with the challenger slipping to the canvas multiple occasions during clinches.
Parker finished the stronger, but several stanzas were challenging to assess. However, former world champion Carl Frampton - providing analysis for the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of hard hitter Benavidez, and Russian star Dmitry Bivol leading the category, the road to world glory - based on this performance - still seems difficult.
Ricky Hatton Memorial Fuels All-Manchester Contest
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a outstanding all-Manchester fight to secure the European light heavyweight title.
The arena grew hushed for a extremely emotional tribute ahead of the contest as ten bells tolled in remembrance of Manchester's own Ricky Hatton, who died aged 46 in September.
It was the initial significant broadcast boxing event in the city since Hatton's death. As the concluding sound disappeared, the quiet transitioned to a shout of "there's just one Hatton".
The competition within the ring equaled the feeling. The eventual winner was floored by a significant blow squarely on the chin in the early round, rising shakily to his position on the count of eight.
But the red-colored equipment of the fighter soon advanced again. On the opposite side, Rea - in opposing blue - was injured quickly, noticeable damage forming under his orbital area as the fighters landed punishing blows.
Rea, 27, landed power punches but Arthur, thirty-four, matched the intensity with powerful upward punches as the pace rarely dropped over the full distance.
Arthur edged the decision with scoring tallies of 114-114, narrow lead and wider gap, but the two athletes were relentless and full of heart, everything their inspiration the legend embodied.
