UK light heavyweight Joshua Buatsi earned a win yet unimpressive debut to his career under fresh promotional backing with a decision win over Parker in the Manchester arena.
The Olympic medal winner's punch output likely gained him a judges' verdict in a close 10-round bout at the boxing arena.
But the challenger landed significant shots, delivering effective clean blows in a contest where the approaches never quite clicked, with frequent clinching marring the action.
Two judges scored it 96-94 in favor to the winner, with the final judge a even score.
"It wasn't my best showing but how do champions respond? They prevail," Buatsi stated in the ring as he was met by disapproval from the audience.
The Londoner bounced back after his first professional defeat - an memorable fight with Callum Smith in February - to earn a twentieth professional win.
Various analysts felt Parker, 31, deserved the victory but the Derbyshire fighter suffered the second setback of his 28-match career.
Buatsi Earns Victory in Slow Affair
The fighter's advancement has plateaued in recent years through promotional disputes and extended periods of inactivity.
Once tipped as the rising talent of the British fight scene, he now stands trying to realize his potential - maybe in what appears to be a final roll of the dice - under new promotional backing.
He began cautiously, with the two boxers willing to be aggressive in a tentative early stages.
Parker, whose only previous defeat came at super-middleweight against John Ryder in two years ago after suffering a hand injury in the contest, was making just his second fight at light heavyweight.
By the fight's midpoint, Parker had kept it close, creating difficulties for Buatsi, who operated with a tight guard to edge the better periods.
The crowd's patience diminished because of constant clinching, with Parker slipping to the canvas various instances during close exchanges.
The underdog closed well, but multiple periods were difficult to score. Although, ex-champion Carl Frampton - commentating on the broadcast network - had it significantly in favor for the challenger, awarding Buatsi just only one stanza.
The victor advances, but with the likes of heavy hitter Benavidez, and Russian champion Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Motivates All-Manchester Battle
In the co-main event, Lyndon Arthur overcame Bradley Rea by split-decision in a outstanding all-Manchester fight to capture the continental belt.
The arena grew hushed for a extremely emotional tribute before the fight as 10 bells sounded in remembrance of Manchester's own Ricky Hatton, who died 46 years old in last month.
It was the first major televised match card in the urban center since Hatton's passing. As the concluding sound disappeared, the stillness transitioned to a shout of "there's only one Hatton".
The fighting within the ring equaled the feeling. The eventual winner was floored by a significant blow flush on the jaw in the initial stage, rising shakily to his footing on the eight count.
But the Manchester United-red attire of the fighter soon came forward again. From the other corner, Rea - in opposing blue - was marked up early, heavy swelling appearing under his orbital area as the duo landed hard punches.
Rea, 27, landed power punches but the champion, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over twelve rounds.
Arthur barely secured the result with official scores of draw, close margin and 115-112, but each competitor were persistent and brave, exactly what their inspiration the legend embodied.
