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We demonstrate by 3D numerical calculations that the interaction of a single quantum emitter with the electromagnetic field is both enhanced and directed by a nano-optical Yagi-Uda antenna. The single emitter is coupled in the near field to the resonant plasmon mode of the feed element, enhancing both excitation and emission rates. The angular emission of the coupled system is highly directed and determined by the antenna mode. Arbitrary control over the main direction of emission is obtained, regardless of the orientation of the emitter. The directivity is even more increased by the presence of a dielectric substrate, making such antennas a promising candidate for compact easy-to-address planar sensors.