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"We were poor," Munster told former Storm teammate Cameron Smith on Nine's coverage.
"Didn't really care who we had out. Still had a good enough team to give the Panthers a shake.
"We can whinge about the weather or whinge about the slippery ball, but we were poor tonight and that's not us, especially against a good side (in) Penrith.
"We have to go back to the drawing board and play a lot better against the Cowboys, otherwise it'll be the same result.
"Pretty disappointing result, and my performance, as well."
When the Storm hit back through a Nick Meaney try in the 18th minute, the hopes of Melbourne fans were renewed.
But what followed was relentless Penrith attack and little Melbourne resolve.
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"We kept getting into the pressure kind of footy we wanted to play, but we just kept giving them piggybacks and letting them out of their own end," Munster said.
"When you're doing that against Penrith they're going to make you pay… when Penrith's got 60 per cent of the ball they're going to put a lot of points on you, and they did tonight.
"We were poor. We looked like an under-12s team.
"We need to go back to the drawing board.
"I can't wait for next week. Far out."
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