A second-half double from substitute Craig Dunn helped Ross County reach the next round of the Challenge Cup.
The Dingwall side went ahead after 21 minutes when Andy Dowie met Michael Gardyne's corner with a strong header.
East Fife almost levelled in the 48th minute but Ryan Blackadder's free-kick swerved inches wide.
Dunn latched on to a flick from Fergus Tiernan before driving the ball past John Dodds and he grabbed a second when he ran the ball into an empty net.
East Fife: Dodds, David Ross, Jonathan Smart, Courts, Smith, Mitchell, Fortune, Jablonski, Blackadder, O'Reilly (Gordon 80), Craig Smart. Subs Not Used: Linton, Doyle, McGowan, Iain Ross.
Booked: Craig Smart.
Ross County: Malin, Niven, Dowie, Keddie (McCulloch 75), Robertson, Gardyn, Irvine, Tiernan, McKinlay (Scott 70), Higgins (Gunn 63), Cowie. Subs Not Used: Anderson, Ridgers.
Booked: Gardyn, Higgins, Keddie. Goals: Dowie 21, Gunn 70, 72.
Ref: M Tumilty