British light-heavyweight Joshua Buatsi secured a victory yet underwhelming start to his career under new promoters with a unanimous decision over Parker in Manchester.
The Olympic bronze medallist's activity level appeared to earn him a judges' verdict in a close ten-round bout at the Co-op Live Arena.
But the challenger landed significant shots, connecting with powerful individual punches in a match where the techniques didn't complement each other, with excessive holding spoiling the contest.
The officials scored it 96-94 to Buatsi, with the remaining official a 95-95 draw.
"It wasn't my finest display but what do champions do? They win," the victor said in the ring as he was met by boos from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in February - to claim a twentieth professional win.
Various analysts felt the challenger, 31, merited the win but the Derbyshire fighter experienced the second setback of his 28-match career.
The Champion Claims Victory in Dull Match
His career development has slowed in recent years through management issues and long spells of inactivity.
Once tipped as the next star of the British fight scene, he now is positioned trying to fulfil that early promise - maybe in what seems like a ultimate opportunity - under fresh management.
He started carefully, with the two boxers ready to overcommit in a tentative early stages.
Parker, whose single earlier setback came at super-middleweight against his former opponent in two years ago after breaking his hand during the bout, was making just his second fight at light heavyweight.
By the halfway stage, Parker had made it competitive, creating difficulties for the favorite, who utilized a tight guard to edge the cleaner rounds.
The audience's tolerance diminished amid constant clinching, with Parker falling to the floor several times during close exchanges.
Parker ended stronger, but many rounds were challenging to assess. Nevertheless, previous titleholder the boxing analyst - providing analysis for Dazn - had it particularly wide for the challenger, awarding Buatsi just a single round.
Buatsi progresses, but with the likes of power puncher Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Memorial Inspires Local Rivalry Battle
In the supporting bout, Lyndon Arthur beat Bradley Rea by close verdict in a terrific Manchester vs Manchester battle to win the European light heavyweight title.
The arena fell silent for a deeply poignant memorial ahead of the contest as a bell ceremony tolled in remembrance of local hero Ricky Hatton, who passed away at age 46 in recently.
It was the first major televised match card in the urban center since the passing of Hatton. As the concluding sound ended, the quiet transitioned to a shout of "there's just one Ricky Hatton".
The action within the ring matched the feeling. The eventual winner was sent to the canvas by a significant blow squarely on the chin in the second round, rising shakily to his feet on the count of eight.
But the red-colored equipment of the fighter soon advanced again. Across the ring, Rea - in opposing blue - was marked up soon, significant bruising appearing under his eye as the duo exchanged punishing blows.
The challenger, 27, delivered effective strikes but Arthur, thirty-four, matched the intensity with stinging uppercuts as the action rarely dropped over twelve rounds.
The victor edged the decision with official scores of even score, close margin and 115-112, but each competitor were determined and brave, all the qualities their idol Hatton stood for.
