UK light heavyweight Joshua Buatsi earned a win yet underwhelming debut to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level seemingly secured him a split decision in a competitive ten-round bout at the Co-op Live Arena.
But the challenger had his moments, landing some telling single shots in a fight where the approaches failed to mesh, with constant grabbing spoiling the action.
Two judges had it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my greatest performance but how do champions respond? They win," the victor commented in the ring as he was met by disapproval from the crowd.
The Londoner returned to winning ways after his initial pro loss - an thrilling contest with Callum Smith in February - to earn a 20th career victory.
Several boxing experts felt the challenger, thirty-one, should have been awarded the victory but the contender endured the second defeat of his 28-match professional journey.
Buatsi Earns Triumph in Slow Match
Buatsi's progress has stalled in recent years through promotional disputes and extended periods of inactivity.
Previously predicted as the rising talent of British boxing, he now finds himself trying to achieve expectations - possibly in what appears to be a ultimate opportunity - under recent support.
He opened tentatively, with both competitors willing to be aggressive in a tentative opening few rounds.
Parker, whose sole prior loss came at super middleweight against his former opponent in two years ago after damaging his hand in the contest, was participating in his second fight at light heavyweight.
By the fight's midpoint, the underdog had kept it close, causing problems for Buatsi, who worked behind a solid defense to edge the better stanzas.
The spectators' acceptance diminished because of regular grabbing, with the challenger slipping to the canvas various instances during close exchanges.
Parker finished the stronger, but many rounds were challenging to assess. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it particularly wide for Parker, giving Buatsi just one round.
The victor progresses, but with the caliber of heavy hitter Benavidez, and Russian champion Bivol ruling the division, the journey to titles - based on this performance - still looks steep.
Hatton Memorial Fuels Local Rivalry Fight
In the secondary fight, Lyndon Arthur beat Rea by divided decision in a excellent Manchester vs Manchester battle to win the continental belt.
The stadium grew hushed for a profoundly moving tribute before the fight as a bell ceremony tolled in memory of local hero Hatton, who died aged 46 in recently.
It was the first major televised match card in the urban center since Hatton's passing. As the final chime disappeared, the stillness transitioned to a roar of "there's just one Ricky Hatton".
The competition during the bout equaled the emotion. Arthur was sent to the canvas by a left hook squarely on the jaw in the second round, getting up unsteadily to his position on the eight count.
But the traditional red shorts of Arthur soon advanced again. Across the ring, the opponent - in rival City blue - was damaged soon, noticeable damage appearing under his face as the pair traded powerful shots.
Rea, 27, connected with strong blows but Arthur, 34, fought fire with fire with effective uppercuts as the intensity seldom decreased over 12 rounds.
The victor barely secured the verdict with scoring tallies of draw, close margin and wider gap, but the two athletes were determined and courageous, everything their hero the legend stood for.
