The dismissal of Cristian Ansaldi on the stroke of half-time proved Rubin's undoing, with Tarasov hitting the target seven minutes into the second half.
The win lifts Lokomotiv level on points with second-placed Zenit St. Petersburg and three behind leaders Terek Grozny.
In the day's other match, Kuban Krasnodar twice came from behind to claim a 2-2 draw at home to Spartak Moscow.
The visitors took the lead first through Aiden McGeady and then Emmanuel Emenike, but those goals were cancelled out by Artem Fidler and Aras Ozbiliz. Kuban Krasnodar lie sixth in the table, above their opponents on goal difference.