Rosberg makes it seven wins in a row

SOCHI, Russia, May 1 (Reuters) - Formula One championship leader Nico Rosberg chalked up his seventh win in a row at the Russian Grand Prix on Sunday with team mate Lewis Hamilton fighting back from 10th on the grid to seal a Mercedes one-two finish.   In a race that started with chaos, and Ferrari's Sebastian Vettel being shunted into the wall by Red Bull's Russian Daniil Kvyat, Rosberg had an untroubled afternoon from pole to chequered flag for his 18th career win.   The German equalled the achievement of compatriot Michael Schumacher in winning seven successive races, with only Vettel (nine in 2013 with Red Bull) and the late Italian Alberto Ascari ahead of them.  

Hamilton was 25 seconds behind Rosberg with Ferrari's Kimi Raikkonen finishing third after winning a battle with fellow-Finn Valtteri Bottas, who started on the front row, in the Williams.   Rosberg, who won the last three races of 2015 and now the first four of 2016, leads triple world champion Hamilton by 43 points in the standings with 17 races remaining.