Russ' 41st-minute goal was enough for victory, but Frankfurt had their 38-year-old custodian to thank for keeping a priceless clean sheet.
He even saved a penalty from Michel Bastos as the Eagles moved back up the table with a vital victory considering results elsewhere, leaving Schalke at risk of losing fourth spot in the Bundesliga to Freiburg tomorrow.
Nikolov is in the Frankfurt goal until the end of the season after Kevin Trapp broke his hand, yet he demonstrated how reliant he can be.
The Macedonian was in the thick of the action immediately, denying Bastos and Raffael as Schalke built up some good early pressure.
He then prevented Bastos from giving Schalke the lead in the 24th minute by saving a penalty after Stefan Aigner had handled the ball inside the area.
That came shortly after Takashi Inui had hit the crossbar at the other end with Frankurt's first dangerous attack.
The next Frankfurt attack saw the 17-year-old Marc Stendera also hit the crossbar before he set up Russ for the only goal of the game.
His curling free-kick was headed past Hildebrand, who stood motionless on the goal line.
The second half started like the first with Schalke on the attack, but Nikolov was always there to deny them.
He made quick-fire saves to deny Julian Draxler and Teemu Pukki as the Royal Blues searched for an equaliser.
But as the visitors tired, Frankfurt had two good chances to finish them off with Hildebrand saving from Inui with his foot and Karim Matmour sending a header wide of the target from another Stendera set piece.