British light heavyweight Joshua Buatsi earned a win yet disappointing debut to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level likely gained him a judges' verdict in a close ten-round contest at the boxing arena.
But Parker landed significant shots, connecting with powerful clean blows in a fight where the approaches never quite clicked, with excessive holding disrupting the fight.
The officials judged it 96-94 to Buatsi, with the third a even score.
"It wasn't my finest showing but what do champions do? They prevail," Buatsi commented in the ring as he was greeted with negative reactions from the crowd.
The British fighter returned to winning ways after his initial pro loss - an epic battle with his previous opponent in last winter - to earn a 20th career victory.
Several boxing experts felt the challenger, thirty-one, should have been awarded the win but the British boxer endured the second defeat of his 28-bout career.
Buatsi Earns Win in Dull Affair
Buatsi's progress has plateaued in the past few years through contract problems and considerable time of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to fulfil that early promise - perhaps in what appears to be a last chance - under fresh management.
He opened tentatively, with the two boxers prepared to overcommit in a cagey early stages.
Parker, whose only previous defeat came at super middleweight against John Ryder in two years ago after damaging his hand mid-fight, was competing in only his second appearance at light heavyweight.
By the fight's midpoint, the underdog had kept it close, creating difficulties for Buatsi, who utilized a protective stance to edge the more effective rounds.
The audience's tolerance wore thin amid constant clinching, with Parker falling to the floor multiple occasions during grappling.
Parker finished the stronger, but several stanzas were difficult to score. However, ex-champion Carl Frampton - working with Dazn - had it significantly in favor for the challenger, awarding Buatsi just one round.
The victor advances, but with the presence of hard hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - on this evidence - still looks steep.
Hatton Memorial Fuels Manchester Derby Battle
In the supporting bout, Arthur defeated Bradley Rea by divided decision in a outstanding Manchester vs Manchester fight to secure the European light-heavyweight title.
The arena grew hushed for a extremely emotional tribute before the fight as 10 bells sounded in memory of local hero Ricky Hatton, who succumbed at age 46 in recently.
It was the first major televised fight night in the location since Hatton's passing. As the last bell disappeared, the quiet transitioned to a shout of "there's just one Hatton".
The competition during the bout matched the feeling. Arthur was knocked down by a powerful punch directly to the chin in the initial stage, rising shakily to his feet on the eight count.
But the traditional red attire of the fighter soon pressed ahead again. On the opposite side, Rea - in competitive blue - was injured quickly, noticeable damage appearing under his face as the fighters landed powerful shots.
Rea, 27, connected with strong blows but Arthur, thirty-four, responded in kind with powerful upward punches as the pace seldom decreased over 12 rounds.
The victor edged the decision with official scores of even score, narrow lead and wider gap, but the two athletes were relentless and brave, everything their idol Hatton embodied.
