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Russia signed off with a 68-22 defeat by Australia in Nelson on Saturday, putting in a spirited second-half display. Their other defeats came against Ireland, Italy and the United States.
"I took this decision a long time ago," Nerush said in the wake of Saturday's defeat. "Even if we won the Webb Ellis Cup I would not have changed my mind.
"When I took up the team our main target was to qualify for the World Cup. We have accomplished this goal, so I deem my job to be done.
"Now it's time to step aside as new people should come to the team to bring new emotions and energy. Our team should move forward.
"There was a huge expectation on us against the United States, we were expected to win, and the whole competition was really tough for us.
"But it is a great tournament and we have touched it with our own hands. I am grateful to my players who have shown the strong will to win and great character."
Nerush took over the national team at the end of 2008 but continued his role as coach of Russian club VVA-Podmoskovye, which he will concentrate on full-time from now.
"The national championship has not yet finished in Russia. Once it comes to an end I will decide what my next occupation will be," he said.
"What I am confident about right now is that it is important to develop young talent in Russia."