After a struggle the woman managed to strike the attacker in the face with her torch a number of times before breaking free and running for help.
The PSNI immediately responded to search for the attacker but he had fled the scene.
Detective Inspector Ross Olphert said: “Understandably the victim has been left traumatised and extremely distressed by this ordeal.
“Our specialist officers are continuing to support her today and a full investigation is underway.
“Attacks like this are an attack on all of us. Women should be free to go about their lives free from any threat,” he added.
The PSNI are appealing to anyone who was in the park on Friday evening to come forward with information.
