2 Selects 1 is faster, why?

If I perform the following 2 selects, the first one is EXTREMELY slow where
the 2nd one is very fast.

(1) Slow

select
o.orderid,
ol.itemcode,
ol.itemname

from
orders o,
orlines ol

where
o.orderid = '1234' and
ol.orderid = o.orderid;

(2) VERY FAST

select
o.orderid,
ol.itemcode,
ol.itemname

from
orders o,
orlines ol

where
o.orderid = '1234' and
ol.orderid = '1234'

Why would 2 be so much faster? I have ran the EXPLAIN on this and index
scans are being used.

NOTE: The actual queries return more information than this, but the
fundamental change shown above seems to give me the instant response I am
looking for. (1) takes about 60 seconds to run and (2) takes 3-5 seconds to
run.

Thanks, Eric