Why is LINQ .Where(predicate).First() faster than .First(predicate)?

Question

I am doing some performance tests and noticed that a LINQ expression like

result = list.First(f => f.Id == i).Property

is slower than

Answer 1

I got the same results: where+first was quicker than first.

As Jon noted, Linq uses lazy evaluation so the performance should be (and is) broadly similar for both methods.

Looking in Reflector, First uses a simple foreach loop to iterate through the collection but Where has a variety of iterators specialised for different collection types (arrays, lists, etc.). Presumably this is what gives Where the small advantage.