Check out eventstats and the first() function:
http://docs.splunk.com/Documentation/Splunk/6.1.3/SearchReference/eventstats
I think you're after something like this:
sourcetype=access* | eventstats dc(session_id) as Visits | stats count as Views, first(Visits) as Visits by uri
If you don't have a session_id logged, consider using the clientip a mashup of client_ip and useragent :
sourcetype=access* | eval uid = clientip + useragent | eventstats dc(uid) as Visits | stats count as Views, first(Visits) as Visits by uri
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