Russian Premier League Wrap: Top two draw as CSKA close gap
Andre Villas-Boas' Zenit side went into the weekend with a one-point advantage over their opponents at the summit, and that remains after Salomon Rondon's 35th-minute opener for the leaders was cancelled out by Sergey Tkachev's equaliser 14 minutes from time on Sunday.
That draw was the ideal result for in-form CSKA, who gained ground on both of their rivals courtesy of a 3-1 win at Amkar Perm on Friday.
The visitors went ahead through Alan Dzagoev's 39th-minute strike but were pegged back on the stroke of half-time by Georgi Peev.
CSKA were not to be denied, however, as second-half strikes from Zoran Tosic and Seydou Doumbia - his 17th league goal of the season - earned them an eighth league win in succession.
The victory leaves them a point behind Lokomotiv and two adrift of Zenit with two matches remaining - including a home fixture with the former on the final day of the campaign.
At the wrong end of the table, Volga's hopes of avoiding automatic relegation were dealt a major blow as Ari's goal after 15 minutes saw them go down 1-0 at home to Krasnodar.
Andrei Karyaka missed a second-half penalty for Volga, who then saw Artur Sarkisov dismissed for a second bookable offence late on.
Volga are now five points adrift of Krylya Sovetov, who were not able to take advantage of their rivals' defeat as they were hammered 4-0 away at Kuban Krasnodar.
Sovetov currently occupy one of the two relegation play-off spots, the other of which is taken up by Ural, who dropped down to 13th after Cesar Navas' strike consigned them to a 1-0 defeat at Rubin Kazan.
That loss allowed Tom Tomsk to leapfrog them into 12th place after a 2-1 win over Spartak Moscow.
Bottom club Anzhi's faint hopes of avoiding automatic relegation remain intact after they saw off Terek Grozny 3-0 on Sunday.
Gadzhi Gadzhiev's men now lie six points behind 14th-placed Sovetov with two matches to go.
Elsewhere, Dinamo Moscow look set to secure a spot in next season's UEFA Europa League after a 3-2 win at Rostov thanks to a brace from Alexei Ionov on Friday.