Axel Witsel scored the decisive goal to move Zenit closer to Russian Premier League glory with a 1-0 home win over lowly Arsenal Tula.
Belgium midfielder Witsel struck in the 17th minute at Stadion Petrovski on Sunday as Andre Villas-Boas' men maintained their eight-point lead over Krasnodar with just five games remaining.
Zenit's win came 24 hours after second-placed Krasnodar had closed the gap at the top to five points with a hard-fought 1-0 home win over Lokomotiv Moscow.
Mauricio Pereyra's penalty eight minutes before the break proved enough for Oleg Kononov's side at Stadion Kuban.
CSKA Moscow extended their advantage over city rivals Dynamo in third with a 2-0 win at another club from the Russian capital - lowly Torpedo Moscow.
Dynamo spurned the opportunity to move back within a point of CSKA when they were surprisingly held to a 2-2 draw at Rostov, despite taking the lead twice.
Amkar Perm took full advantage of Torpedo Moscow's defeat to move off the foot of the table with a 2-1 home win over Terek Grozny.
Arsenal Tula's defeat at Zenit means Amkar are now just three points behind Dmitri Alenichev's men, with a game in hand.
Spartak Moscow moved to within a point of Rubin Kazan in the final UEFA Europa League spot as Quincy Promes' injury-time strike gave them a vital 1-0 win over Rinat Bilyaletdinov's team on Sunday.
Elsewhere, Friday's Premier League fixtures saw Ufa beat Kuban Krasnodar 3-2 and Mordovia Saransk defeat Ural 2-1.
