The 36 year-old, who broke Viktor Onopko's appearance record by winning his 110th cap, opened the scoring from close range after 58 minutes, before Artem Dzyuba sealed victory with 12 minutes to go.
Eugeniu Cebotaru scored for Moldova after 85 minutes but Russia held on for the vital win.
Russia went ahead when Dmitry Kombarov floated in a free kick from the right, which was chested down by Dzyuba straight into the path of Ignashevich and the CSKA Moscow defender lashed the ball past Alexei Koshelev.
Dzyuba doubled the lead in the 78th minute as he scored from close range following a corner to notch up his eighth goal in seven qualifying games.
Cebotaru made it a nervous finish for the visitors but they held on as head coach Leonid Slutskiy recorded his third straight victory since taking over from Fabio Capello.
Russia remain second in Group G on 17 points behind already qualified Austria and will qualify for next summer's European championships if they beat Montenegro in Moscow on Monday. Moldova stay bottom with two points.
(Reporting By Dmitriy Rogovitskiy in Moscow)
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