The 20-year-old passed compatriot and defending champion Olga Kaniskina in the final kilometre to take victory in 1:25.02.
Kaniskina went off quickly and looked a certain winner as she continued to pull clear, leading her fellow Russian by 43 seconds at the 12km mark.
But Lashmanova had timed her race to perfection and closed that gap to 36 seconds by the 14km mark, 24 by the 16km point and 17 with 2km to go before reeling her rival in on the last lap.
Kaniskina, the three-time reigning world champion, took silver, seven seconds back, with China's Qieyang Shenjie taking the bronze.
Kaniskina said: 'It wasn't very lucky for me to lose the race at the last minute, it is difficult for me to deal with. I am very pleased for my team-mate though, she deserved it.
'I wish I walked a bit faster at the finish line.
'It's 50/50 for me, because I am happy because I got the medal but at the same time I am very disappointed in the manner of the finish.'
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