A Goldman Sachs investment banker raped an Irish tourist because he wanted sex on his birthday and “was going to do whatever he had to to get it”, a court has heard.

Jason Lee, 37, was arrested at the luxury home he rented with his wife in the Hamptons, New York, accused of sexually assaulting a woman in the bathroom while her friend and brother partied nearby.

In opening statements at his trial, prosecutor Kerriann Kelly said the well-dressed and attentive defendant appearing in court was far removed from the man encountered by the alleged victim in the early hours of 20 August, 2013 when Mr Lee was celebrating his birthday.

“What you see is not always what you get,” Ms Kelly said. “What she encountered was a man who wanted one thing and one thing only and that was sex… he was going to do whatever he had to do to get it.”

Both defence and prosecution lawyers agreed that Mr Lee met his alleged victim while out at a New York nightclub. She was visiting her brother with a friend, and at closing time Mr Lee invited the Irish group back to his house.

Former New York City investment banker Jason Lee walks with his wife Alicia into Suffolk County Court on Wednesday 8 April, 2015 (AP)

The woman, who was 20 years old at the time, told police that Lee forced his way into the bathroom, pinned her down with his hand over her mouth and raped her.

Police were called and alerted to the woman’s distraught state by her brother, prosecutors said. Officers found Lee hiding around two hours later in the back seat of his Range Rover that was parked outside the house, from where his mobile showed he had made numerous attempts to call taxis.

Mr Lee's lawyer, Andrew Lankler, said the sex was consensual albeit “perhaps regrettable”. He said the woman and her friend had swum in Mr Lee's pool in their underwear, and that the defendant had joined them naked before the alleged rape took place.