JSON Path expression to extract top level only

Question

I have the following JSON:

{
"Results":[
    {
        "PK":9,
        "Name":"Duty Rating",
        "Description":"Length of time motor may be run without stopping for a cooling period",
        "Active":true,
        "TrackHistory":false,
        "LastModifiedDate":"2013-07-04T14:15:36",
        "ResourceUri":"uri",
        "CategoryRef":{
            "PK":19,
            "ID":"ME",
            "Name":"Mechanical",
            "Uuid":null
    }
    }
],
"Total":1

}

When I use the json path expression:$[*]..PK I get all the elements but I only want the top element returned. i.e. PK: 9 not the CategoryRef PK 19. Thanks