When one does an "I'm Feeling Lucky" search, the expectation is to be directed directly to the target of the first result.

One way of doing such a search is with the "btnI" attribute, as with the term "sample" below.

http://www.google.com/search?q=sample&btnI=I'm+Feeling+Lucky

If I try this with the term "sammple" I get the SERP instead.

http://www.google.com/search?q=sammple&btnI=I'm+Feeling+Lucky

A cursory inspection of the html on google's front page appears to also use "btnI". Trying "sammple" with the "I'm Feeling Lucky" button from the google front page seems to redirect as expected.

[2nd URL updated as requested – Tony]