Goals in each half from Danny Lafferty and Junior Ogedi-Uzokwe avenged defeat in the midlands on the opening night of the season as Derry City left Bishopsgate with all three points on this occasion.
Ruaidhri Higgins’ Candystripes move above Dundalk to sixth place in the table while Longford, without a league win now in 21 games, languish nine points adrift at the bottom.
A lightning start from Longford almost brought them the lead after just 14 seconds, Shane Elworthy’s ball over the top catching Derry square.
Dean Williams scampered through to pull a pass back for Aaron McNally whose effort was turned round a post by Nathan Gartside.
But Derry soon grew into the game to dominate, getting their reward with a fine goal on 31 minutes.
Their front two of Junior and James Akintunde dovetailed well in the build-up to open up the home defence.
Junior held the ball up well to find Akintunde who had the composure and vision to pick out wingback Lafferty arriving on the left to crack a low drive to the far corner of the net.
Akintunde might have doubled Derry's lead on 70 minutes with a gilt-edged chance.
Junior's persistence and Evan McLaughlin's incisive pass set up Akintunde who delayed pulling the trigger to allow Aaron Robinson to get back and make a superb block to the shot.
Akintunde made amends with his second assist of the game on 82 minutes, collecting Lafferty’s long ball to turn and play Junior in to slip the ball past Lee Stacey.
Steacy; Elworthy (Chambers, 19), J. Manley, O’Driscoll, Kirk (Dobbs, 57); Dervin, Robinson (O’Brien, 74); R. Manley (Warfield, 74), Grimes, McNally; Williams.
Gartside; Toal, McJannet, Coll; Malone, Thompson; Boyce (Hery, 48), E. McLaughlin (Cole, 76), Lafferty; Akintunde (McGonigle, 83), Ogedi-Uzokwe.
John McLoughlin (Roscommon).