Maguire and Browne made their first starts for the Irish after previously being capped once as substitutes, while Horgan came off the bench for the last 10 minutes of the friendly international.
Striker Maguire, scorer of five goals in the last four games for North End, played 62 minutes before being replaced by Shane Long, while Browne lasted until the 67th minute - he gave way to David Meyler.
Turkey's winning goal came six minutes into the second half, skipper Mehmet Topal getting clear of the Republic's defence to shoot past keeper Colin Doyle.
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This was Ireland's only game of the international break, with Maguire, Browne and Horgan due back at Springfields on Monday morning to commence PNE's build-up to the Good Friday clash with Sheffield Wednesday at Hillsborough.