.NET 4.5 Async vs. TPL

I am starting to read about .NET 4.5 Async but frankly cannot get the most of it yet when to comes to the usage patter. So i will try to get that with a direct question:

I usually use .NET 4 TPL to call expensive Web services and DB calls from inside my ASP.NET application. Seems that i can achieve the same thing with Async. Is this true? When to use which?

Thanks in advance.