A Nathan Cleary sin-binning has helped Manly consign Penrith to their second straight loss after the premiership contenders were shocked 18-10 by the lowly-ranked Sea Eagles on Saturday.
With scores locked at 10-10 with 15 minutes to play, Cleary was ruled by the NRL's bunker to have held Daly Cherry-Evans off the ball as he chased his own grubber kick close to the line.
The NSW halfback was sent to the bin for the professional foul, Trent Hodkinson then slotting over the penalty goal for Manly to take a 12-10 lead at Panthers Stadium.
Manly then took full advantage five minutes later when Jake Trbojevic spun and provided an offload for Hodkinson to buck Manly's four-game losing streak and put space between them and the bottom of the ladder.
But the win came as a cost for Manly, who lost star centre Dylan Walker to a knee injury when he was carried off the field early in the second half.
Walker will go for scans on Monday, but Sea Eagles officials were hopeful the blow only came through contact and there was no structural damage to his anterior cruciate ligament.
Penrith also lost powerful second-rower Viliame Kikau to a knee injury late, in what was only his return match from a medial ligament strain on the same knee earlier in June.
The loss drops the Panthers back to fourth and behind Melbourne on the ladder, after they'd logged four straight wins before their loss to the Roosters last round.
In a match that never really reached any great heights, neither team completed at more than 70 per cent while Manly gave away 10 penalties to Penrith's six.
After they led 8-6 at the break, Penrith invited Manly back into the match when James Fisher-Harris dropped the ball on the first run of the second half and put the Sea Eagles on the attack.
The Sea Eagles made the most of it, when Tom Trbojevic cut out two men to put Matthew Wright over - who injured his shoulder in the process.
It was the fullback's second assist of the match, after he also sent Joel Thompson through a gap for Manly's other try early.