UK light heavyweight Joshua Buatsi earned a win yet unimpressive start to his career under new promoters with a points victory over Parker in Manchester.
The Olympic medal winner's activity level likely gained him a split decision in a close 10-round fight at the Co-op Live Arena.
But the challenger found success, landing some telling individual punches in a contest where the techniques never quite clicked, with frequent clinching spoiling the contest.
The scoring judges scored it 96-94 to Buatsi, with the remaining official a even score.
"It wasn't my greatest display but what defines champions? They win," the victor commented in the ring as he was faced disapproval from the crowd.
The Londoner bounced back after his maiden career setback - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Several boxing experts felt the challenger, 31, deserved the victory but the Derbyshire fighter experienced the second loss of his 28-bout career.
The Champion Claims Triumph in Slow Match
His career development has slowed in recent years through contract problems and extended periods of lack of fights.
Previously predicted as the rising talent of the British fight scene, he now finds himself trying to realize his potential - possibly in what appears to be a last chance - under fresh management.
He started carefully, with the two boxers willing to overcommit in a calculated opening few rounds.
The challenger, whose single earlier setback came at super middleweight against his former opponent in two years ago after damaging his hand mid-fight, was participating in his second appearance at the higher weight class.
By the fight's midpoint, the underdog had kept it close, making life awkward for the favorite, who operated with a tight guard to narrowly win the better stanzas.
The crowd's patience diminished amid frequent holding, with Parker slipping to the canvas several times during clinches.
Parker closed well, but multiple periods were challenging to assess. However, previous titleholder Carl Frampton - working with Dazn - had it significantly in favor for Parker, scoring for Buatsi just a single round.
The victor advances, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the road to world glory - based on this performance - still appears challenging.
Hatton Tribute Inspires All-Manchester Contest
In the supporting bout, Arthur defeated Bradley Rea by close verdict in a terrific local rivalry fight to secure the continental championship.
The stadium became quiet for a extremely emotional tribute before the fight as 10 bells tolled in honor of Manchester's own Ricky Hatton, who succumbed at age 46 in September.
It was the initial significant broadcast fight night in the city since Hatton's passing. As the concluding sound faded, the silence became a chant of "there's only one Hatton".
The competition during the bout equaled the emotion. Arthur was floored by a left hook squarely on the chin in the initial stage, standing uncertainly to his feet on the referee's count.
But the red-colored equipment of Arthur soon advanced again. Across the ring, Rea - in opposing blue - was marked up early, significant bruising developing under his eye as the fighters landed punishing blows.
The challenger, 27, landed power punches but the champion, 34, responded in kind with powerful upward punches as the action seldom decreased over 12 rounds.
The victor narrowly won the verdict with scoring tallies of even score, 115-113 and 115-112, but both fighters were persistent and full of heart, all the qualities their idol Hatton embodied.
