We report the discovery by the HATSouth survey of HATS-3b, a transiting extrasolar planet orbiting a V=12.4 F dwarf star. HATS-3b has a period of P=3.5479days, mass of M_p_=1.07M_J_, and radius of R_p_=1.38R J. Given the radius of the planet, the brightness of the host star, and the stellar rotational velocity (vsini=9.0km/s), this system will make an interesting target for future observations to measure the Rossiter-McLaughlin effect and determine its spin-orbit alignment. We detail the low-/medium-resolution reconnaissance spectroscopy that we are now using to deal with large numbers of transiting planet candidates produced by the HATSouth survey. We show that this important step in discovering planets produces logg and T_eff_ parameters at a precision suitable for efficient candidate vetting, as well as efficiently identifying stellar mass eclipsing binaries with radial velocity semi-amplitudes as low as 1km/s.