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 Manchester.
The Olympic bronze medallist's work rate appeared to earn him a majority decision in a competitive ten-round bout at the Manchester venue.
But the challenger found success, connecting with powerful single shots in a contest where the techniques failed to mesh, with constant grabbing marring the action.
The officials judged it 96-94 in favor to Buatsi, with the third a even score.
"It wasn't my greatest performance but what do champions do? They succeed," the victor commented in the ring as he was greeted with boos from the crowd.
The British fighter got back to winning after his maiden career setback - an epic battle with his previous opponent in February - to secure a 20th career victory.
Several boxing experts thought the challenger, thirty-one, merited the win but the British boxer endured the second setback of his 28-match career.
The Champion Earns Win in Slow Affair
Buatsi's progress has stalled in the past few years through promotional disputes and extended periods of inactivity.
Previously predicted as the next star of UK boxing, he now finds himself trying to fulfil that early promise - maybe in what appears to be a final roll of the dice - under recent support.
He started carefully, with neither fighter ready to overcommit in a cagey early stages.
The challenger, whose sole prior loss came at super middleweight against John Ryder in 2022 after damaging his hand during the bout, was making just his second bout at the higher weight class.
By the halfway stage, Parker had made it competitive, making life awkward for the favorite, who worked behind a protective stance to narrowly win the better stanzas.
The crowd's patience wore thin during constant clinching, with the challenger slipping to the canvas several times during close exchanges.
Parker finished the stronger, but many rounds were difficult to score. However, previous titleholder Carl Frampton - providing analysis for the broadcast network - had it significantly in favor for Parker, scoring for Buatsi just only one stanza.
The victor moves on, but with the likes of heavy hitter Benavidez, and Russian star Dmitry Bivol dominating the weight class, the path to championship success - judging by this showing - still appears challenging.
Hatton Tribute Inspires All-Manchester Fight
In the supporting bout, Lyndon Arthur defeated Rea by close verdict in a excellent Manchester vs Manchester fight to win the European light heavyweight title.
The venue fell silent for a profoundly moving tribute prior to the bout as ten bells rang in honor of Manchester's own Hatton, who passed away at age 46 in last month.
It was the first major televised match card in the city since Hatton's passing. As the final chime faded, the silence became a shout of "only one Hatton".
The competition inside the ropes equaled the emotion. The eventual winner was knocked down by a left hook squarely on the face in the early round, getting up unsteadily to his position on the count of eight.
But the Manchester United-red equipment of the fighter soon advanced again. From the other corner, Rea - in opposing blue - was damaged early, significant bruising developing under his face as the duo traded hard punches.
Rea, 27, landed power punches but the champion, 34, responded in kind with powerful upward punches as the pace hardly diminished over twelve rounds.
The victor barely secured the result with official scores of even score, narrow lead and wider gap, but both fighters were persistent and courageous, all the qualities their idol the legend represented.
