Per Baseball Reference, last game at RFK in 2007 was on Sept. 23rd, Nats against Phillies, Nats winning 5 to 3. That was the odd year the Nats came in 4th, amidst the multiple last place finishes.
http://www.baseball-reference.com/boxes/WAS/WAS200709230.shtml
There are, in retrospect, a...