British light-heavyweight Joshua Buatsi earned a win yet underwhelming start to life under recent management with a unanimous decision over Parker in Manchester.
The Olympic medal winner's activity level appeared to earn him a judges' verdict in a close 10-round contest at the Manchester venue.
But the challenger landed significant shots, connecting with powerful clean blows in a contest where the approaches failed to mesh, with constant grabbing marring the contest.
The scoring judges judged it 96-94 in favor to Buatsi, with the remaining official a 95-95.
"It wasn't my best performance but what defines champions? They succeed," Buatsi commented in the arena as he was faced negative reactions from the spectators.
The Londoner returned to winning ways after his initial pro loss - an memorable fight with his previous opponent in last winter - to secure a 20th career victory.
Various analysts felt Parker, 31, merited the win but the British boxer endured the second loss of his 28-bout career.
The Champion Secures Victory in Uneventful Match
The fighter's advancement has slowed in the past few years through contract problems and long spells of inactivity.
Once tipped as the future of the British fight scene, he now stands trying to realize his potential - possibly in what seems like a last chance - under fresh management.
He opened tentatively, with the two boxers willing to overcommit in a cagey opening few rounds.
The challenger, whose single earlier setback came at super-middleweight against John Ryder in two years ago after suffering a hand injury during the bout, was competing in only his second bout at light heavyweight.
By the middle rounds, the underdog had made it competitive, making life awkward for Buatsi, who worked behind a solid defense to barely take the more effective rounds.
The crowd's patience diminished amid regular grabbing, with the challenger slipping to the canvas various instances during grappling.
The underdog finished the stronger, but many rounds were challenging to assess. Nevertheless, 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 presence of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - based on this performance - still seems difficult.
Ricky Hatton Homage Motivates All-Manchester Fight
In the secondary fight, Lyndon Arthur overcame Bradley Rea by divided decision in a outstanding all-Manchester contest to win the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving tribute before the fight as ten bells rang in honor of local hero Ricky Hatton, who succumbed aged 46 in recently.
It was the premier televised match card in the urban center since Hatton's death. As the last bell faded, the silence became a shout of "there's only one Ricky Hatton".
The fighting during the bout matched the feeling. The eventual winner was knocked down by a powerful punch squarely on the chin in the initial stage, getting up unsteadily to his feet on the eight count.
But the Manchester United-red shorts of the fighter soon came forward again. On the opposite side, Rea - in opposing blue - was marked up early, noticeable damage appearing under his face as the duo exchanged punishing blows.
Rea, 27, connected with strong blows but the champion, 34, matched the intensity with powerful upward punches as the action hardly diminished over twelve rounds.
Arthur narrowly won the result with scoring tallies of even score, 115-113 and clearer margin, but each competitor were persistent and full of heart, everything their idol the legend stood for.
