By dint of superior engagement, the mind and intelligence become subordinate to the soul and thus automatically controlled. When the mind and intelligence are engaged in Krishna's service, the senses follow. Trying to conquer the senses artificially is extremely difficult. Krishna explains that even one of the senses can lead a transcendentalist to lose his renunciation.
Lectures from a disciple Vol 1, Sadhana, Pg 400, 3rd paragraph