British light heavyweight Joshua Buatsi made a winning yet unimpressive start to his career under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's punch output appeared to earn him a split decision in a competitive ten-round contest at the Co-op Live Arena.
But Parker had his moments, connecting with powerful individual punches in a fight where the techniques didn't complement each other, with excessive holding disrupting the contest.
The scoring judges had it 96-94 for to the winner, with the third a even score.
"It wasn't my best showing but what defines champions? They succeed," the victor said in the ringside as he was faced boos from the crowd.
The British fighter got back to winning after his initial pro loss - an memorable fight with Callum Smith in February - to claim a 20th career victory.
Various analysts believed the challenger, 31, deserved the victory but the British boxer experienced the second loss of his 28-bout career.
The Champion Claims Victory in Slow Match
His career development has stalled in recent years through management issues and long spells of inactivity.
Previously predicted as the rising talent of the British fight scene, he now stands trying to realize his potential - maybe in what feels like a last chance - under fresh management.
He started carefully, with both competitors willing to be aggressive in a cagey 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 in the contest, was participating in his second appearance at the higher weight class.
By the fight's midpoint, Parker had stayed in contention, making life awkward for the favorite, who worked behind a protective stance to edge the cleaner stanzas.
The audience's tolerance diminished amid regular grabbing, with the challenger slipping to the canvas multiple occasions during close exchanges.
Parker finished the stronger, but several stanzas were hard to judge. Although, previous titleholder the boxing analyst - commentating on Dazn - had it strongly leaning for the challenger, scoring for Buatsi just only one stanza.
Buatsi advances, but with the presence of power puncher Benavidez, and Russian star Dmitry Bivol ruling the division, the road to world glory - judging by this showing - still appears challenging.
Ricky Hatton Memorial Inspires Local Rivalry Contest
In the secondary fight, Lyndon Arthur defeated Rea by split-decision in a outstanding Manchester vs Manchester fight to capture the European light-heavyweight title.
The arena grew hushed for a extremely emotional homage before the fight as a bell ceremony sounded in remembrance of Manchester's own Ricky Hatton, who succumbed aged 46 in last month.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the concluding sound disappeared, the quiet transitioned to a roar of "only one Hatton".
The competition inside the ropes reflected the emotion. Arthur was floored by a left hook directly to the chin in the initial stage, getting up unsteadily to his feet on the referee's count.
But the traditional red attire of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was damaged soon, noticeable damage appearing under his face as the fighters traded powerful shots.
Rea, 27, connected with strong blows but the champion, thirty-four, fought fire with fire with effective uppercuts as the pace seldom decreased over twelve rounds.
Arthur barely secured the decision with official scores of draw, narrow lead and clearer margin, but both fighters were persistent and brave, exactly what their idol Hatton represented.
