The approach we are taking to look at this question is straightforward. The starting pitcher leaves the game with the lead (after pitching at least five innings). If the bullpen loses the lead resulting in either a loss or a no-decision for the starting pitcher, he is considered to have been let down.
First, let's look at the major leagues as a whole. When a pitcher leaves the game after five or more innings with a lead, he can expect to get a win 80% of the time. In 2006 the starter left the game in this situation 1,982 times and recorded 1,583 wins. That's 80%.
Here are the pitchers with the most "blown wins" by his bullpen in 2006. Each of them could easily have had 3 or 4 more wins with normal bullpen support:
| Name | Record | Blown Wins |
| Derek Lowe, Dodgers | 16-8 | 6 |
| Jeff Francis, Rockies | 13-11 | 6 |
| Casey Fossum, Devil Rays | 6-6 | 6 |
| Luke Hudson, Royals | 7-6 | 6 |
With normal bullpen support Lowe wins 19, Francis wins 15+ while Fossum and Hudson both get into double digits.
Six pitchers had 10 or more leads passed to their bullpens and received flawless support. They are:
| Name | Record | Wins Preserved |
| Brad Penny, Dodgers | 16-9 | 15 for 15 |
| Brandon Webb, Diamondbacks | 16-8 | 15 for 15 |
| Mike Mussina, Yankees | 15-7 | 14 for 14 |
| Joe Blanton, A's | 16-12 | 14 for 14 |
| Ramon Ortiz, Nationals | 11-16 | 10 for 10 |
| Francisco Liriano, Twins | 12-3 | 10 for 10 |
Penny, Webb and Lowe tied with three other pitchers for the National League lead in wins in 2006. Clearly it was Lowe who should have won this. With average bullpen support (from the same bullpen, no less) Lowe would have had six more wins than Penny (Lowe with 19 and Penny with 13).