If Mars were tidally locked to the Sun, what would the temperatures on its surface be like? Since there's very little atmosphere on Mars, it doesn't matter much whether the Sun is in the zenith or hanging just above the horizon: without the atmospheric "filter," the sunlight would have roughly the same effect on all sunlight areas.

What would the temperatures be like on the sunlit portion of the planet?
Tidal lock would mean only one side of Mars would be exposed to solar irradiation, so its temperature would be mostly defined by the equilibrium between the energy received from the Sun and the black-body radiation.

Because of the orbit eccentricity, solar irradiation reaching Martian surface varies between 493 and 717 W/m² (source). According to Stefan-Boltzmann law, the temperature required for the black-body radiation to match these levels will vary between 305 and 335 K (32°C an 62°C), respectively.

Such temperatures will be reached in the area directly facing the Sun (so the Sun is seen in zenith), and gradually decline towards the background radiation temperature of space (about 3K) when approaching the dark side (where the Sun is just barely above the horizon). Such temperature distribution is due to the angle of incidence, not to the atmospheric "filter" or lack thereof.