An injury-time goal from Igor Pikushchak and strong goalkeeping gave Amkar a 2-1 away win over Lokomotiv Moscow on Friday.
Slaven Bilic's Lokomotiv look set slip further away from the Russian Premier League leaders with the defeat, which leaves the Railwaymen eight points adrift of table-toppers Anzhi after a four-game winless run. Amkar move up a place to ninth.
Amkar opened the score on 25 minutes when their captain Georgi Peev received the ball in the center of the box and lashed it into the top-right corner of Dario Kresic’s goal.
Ex-Tottenham Hotspur forward Roman Pavlyuchenko equalized 10 minutes later when he headed in Andrei Yeshchenko’s pinpoint cross from the right wing.
In stoppage time, Peev hit the bar with a stinging shot from outside the area, and Pikushchak showed quick reactions to slam in the rebound.
"Desire more than anything, and luck," Peev said when asked how Amkar had won.
"Of course we weren't 100 percent confident that we'd win, we were playing against a good team anyway, a top team."
Bilic said Lokomotiv's performance had been good enough for victory.
"We're all disappointed. We absolutely didn't deserve a defeat, we should have won," he said.
"Inaccuracy and a lack of luck were the reasons for a result like this one, although I've not once blamed luck in my career."
The winner followed a number of good chances for Lokomotiv and rising tensions between the teams.
Pikushchak had an early chance on four minutes when he connected with an Alexander Kolomeitsev cross, but Kresic denied him with a reaction save.
Amkar goalkeeper Sergei Narubin denied Lokomotiv 15 minutes when he parried a 20-yard shot by Lokomotiv midfielder Dmitry Tarasov.
Narubin came under severe pressure in the middle of second half, first stopping a powerful shot from Senegalese striker Dame N’Doye at the near post.
Narubin then made two short-range saves from Lokomotiv attacks before ex-Manchester City forward Felipo Caicedo bumped into Narubin provoking a rumble in Amkar’s box.
Caicedo had an excellent chance to give Lokomotiv the lead a minute from time, but his accurate strike was stopped by Narubin's quick reactions.
Later Friday, FC Kuban host FC Rostov.
On Saturday, Unai Emery’s Spartak Moscow face Mordovia Saransk, bottom-placed FC Volga play FC Krasnodar and reigning champions Zenit travel to Vladikavkaz to face Alania.
Sunday sees Rubin Kazan host Anzhi and surprise package Terek Grozny meet second-placed CSKA Moscow, before Dan Petrescu’s Dynamo Moscow take on Krylya Sovetov.