Well, 11 years and 1 day. To be precise.
On the 12th of August in 2001, Derek Lowe pitched to one Oriole to earn his 24th save of the season. Then he 1) lost his job as closer, and b) became a starting pitcher. For a long while, a really good starting pitcher.
Now he's a reliever again. And on the 13th of August in 2012, Derek Lowe pitched four shutout innings against the Texas Rangers and earned his first save in 11 years. Plus.