This paper deals with an important and insufficiently studied problem relating to the ways in which Russia's authorities use electoral process rules in order to enhance their political advantage at the local level. The well-established Duvergerian framework of electoral system analysis applies to a new context: municipal elections in Putin-era St. Petersburg. One of the effects of the "block vote" electoral system, which is currently the most common method used in the St. Petersburg municipal elections, is the sweep effect, wherein a party with a weak majority of support nevertheless is able to win a large number of seats. From the data on election results in St. Petersburg it can be interpreted that the electoral system used gave a significant bonus to the leading party. It is noteworthy that the leading position in some cases was occupied by the opposition parties, which used the bonus provided by the electoral system.