UK light heavyweight Joshua Buatsi secured a victory yet underwhelming beginning to his career under fresh promotional backing with a decision win over Parker in Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a tight ten-round bout at the Manchester venue.
But the challenger landed significant shots, landing some telling individual punches in a fight where the styles failed to mesh, with frequent clinching marring the action.
The officials scored it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They win," Buatsi stated in the ringside as he was met by disapproval from the audience.
The British fighter bounced back after his maiden career setback - an thrilling contest with his previous opponent in last winter - to claim a twentieth professional win.
Some ringside observers thought the challenger, 31, merited the decision but the Derbyshire fighter experienced the second setback of his 28-bout career.
The Champion Earns Victory in Slow Affair
The fighter's advancement has slowed in recent years through contract problems and long spells of lack of fights.
Earlier forecast as the future of British boxing, he now stands trying to realize his potential - perhaps in what appears to be a last chance - under recent support.
He opened tentatively, with the two boxers ready to be aggressive in a calculated opening few rounds.
Parker, whose sole prior loss came at super middleweight against John Ryder in two years ago after breaking his hand in the contest, was participating in his second bout at light heavyweight.
By the fight's midpoint, the underdog had stayed in contention, causing problems for Buatsi, who utilized a tight guard to barely take the better rounds.
The spectators' acceptance diminished because of constant clinching, with the challenger slipping to the canvas multiple occasions during close exchanges.
The underdog closed well, but many rounds were challenging to assess. Nevertheless, ex-champion Carl Frampton - providing analysis for Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor progresses, but with the presence of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the journey to titles - based on this performance - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the secondary fight, Lyndon Arthur beat Rea by close verdict in a excellent Manchester vs Manchester battle to win the European light heavyweight belt.
The venue grew hushed for a profoundly moving homage prior to the bout as a bell ceremony tolled in memory of the city's native Ricky Hatton, who died at age 46 in last month.
It was the premier televised fight night in the urban center since the passing of Hatton. As the final chime ended, the silence became a chant of "only one Hatton".
The competition during the bout matched the feeling. Arthur was sent to the canvas by a left hook flush on the jaw in the early round, standing uncertainly to his footing on the count of eight.
But the traditional red shorts of Arthur soon advanced again. From the other corner, Rea - in opposing blue - was marked up soon, heavy swelling developing under his eye as the fighters landed powerful shots.
The challenger, 27, delivered effective strikes but the champion, thirty-four, matched the intensity with effective uppercuts as the action rarely dropped over the full distance.
The victor barely secured the decision with official scores of draw, close margin and wider gap, but the two athletes were determined and brave, all the qualities their inspiration Hatton represented.
