Tube passengers are facing the second 24-hour strike in little over a week.
The strike was called in a row over new rotas
A total shutdown had been threatened on New Year's Eve. Forty stations were closed but Transport for London said there was minor disruption.
RMT officials now say they will strike again on Sunday unless a deal is reached in a dispute over new rotas.
They also warned of another ballot over "blatant breaches of safety" during the weekend strike - claims strenuously denied by London Underground (LU).
Most of the stations that closed were outside the central area, and other stations further out and above ground were left unstaffed with their ticket barriers open.
RMT General Secretary Bob Crow accused LU of keeping stations open with insufficient staff to cope with an emergency and using manager and office staff without proper training.
He said Tube drivers and signal workers may be balloted for action short of strikes over the alleged safety lapses.
But an LU spokesman said there was no truth in these allegations
"The strike did not really materialise," he said.
'More strikes to come'
"The RMT leadership are trying to explain away the fact that they lost the argument with London Underground staff who did not agree that it made sense to strike against ordinary Londoners on New Year's Eve."
London Mayor Ken Livingstone told BBC London he predicted several more strikes by the RMT who, he claimed, were left red-faced when a majority turned up for work on New Year's Eve.
"Rather than say they made a mistake, they will dig in and try to make the next strike more effective," he said.
The dispute centres around the introduction of new rotas, which union members fear could lead to the closure of ticket offices, job losses and compromises to safety.
Both sides said they hope to reach an agreement before the next strike scheduled for 1830 GMT on Sunday.