In the first episode of the second series of Sherlock, Cumberbatch's detective matched wits against the iconic character, played by Lara Pulver, who was reimagined as a seductress for the updated show.
The 35-year-old spoke about the challenges of shooting the episode, confirming that Sherlock was charmed by Irene and ultimately fell for her over the course of the instalment.
"Well, he's supposedly an asexual, emotionless machine, and has cut off feelings of attraction or sensory enjoyment or interest in the female form other than to gain information," Cumberbatch told Deadline.
"So it was [about] how to get the audience to believe that you could possibly be in a position that was vulnerable - how could he possibly be feeling something for this woman?" he explained.
"But the thing about [Irene] that is very obvious when you read [the 1891 short story by Arthur Conan Doyle] is Sherlock definitely does fall for her and he does lose his cool," Cumberbatch continued.
"He's no longer the logical machine. He fell for her charms. And so it was a balancing act, but it was so deftly written [by Steven Moffat] that it was so easy to do," he concluded.
Sherlock is expected to begin shooting its third series in January.