Spartak Moscow went eight points clear in the Russian Premier League on Sunday as Alexander Samedov netted the winning goal in their hard-fought 1-0 win against Anzhi Makhachkala.
Reigning champions CSKA Moscow, who trounced bottom-placed Tomsk 4-0 on Saturday, are second equal on points with Zenit St Petersburg, who suffered a 1-0 defeat at Amkar Perm.
"The match was hard, just like I expected," Spartak manager Massimo Carrera said.
"Our lead is comfortable enough but we should never be self-satisfied. There are plenty of matches ahead and we need to keep on working hard."
Spartak dominated but their poor finishing, combined with a good goalkeeping display from David Yurchenko, left the 33,000 home crowd disappointed.
But in the 67th minute, the visitors' resistance crumbled when Samedov scored with a close-range header from Dmitry Kombarov's left wing cross.
Amkar gained revenge for their 3-0 defeat at Saint Petersburg in August by beating Zenit thanks to a goal from midfielder Roland Gigolaev in the 33rd minute.
Rostov warmed up for Thursday's Europa League last-16 return-leg at Manchester United with a disappointing 0-0 draw at home to Terek Grozny.
"Today we lacked speed, freshness and aggression in attack as we had too little time for recovery after the match with Man Utd on Thursday in the first leg," said Rostov manager Ivan Daniliants.
"On Thursday, against Manchester United, everything will be completely different."