Lizzy Yarnold will head into the final day of the Olympic women's skeleton competition in Sochi with almost a half second lead over American Noelle Pikus-Pace.

Britain's gold medal favourite clocked 58.46 seconds on her second run to lead by 0.44secs from Pikus-Pace and by 0.55secs from Russian challenger Elena Nikitina going into Friday's final two runs at the Sanki Sliding Center.

Yarnold's first run was marginally quicker at 58.43secs - a track record - but after the first run she only led by 0.05 of a second from Nikitina, who fell away a little in the lower part of her second run.

The result of the second heat was subject to a protest by the Australian team, although it did not involve Yarnold.

The Australians were protesting about a push-start facility in the proximity of the Olympic track, upon which Russian athletes were practising in between runs.

Under IOC rules, any facility situated within the Olympic zone must be made accessible to all nations.

Although the facility was deemed to be outside the zone at an official rules meeting on Wednesday, the Australians maintain that the Russians' use of it in between runs contradicts that ruling.