Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Date | Tournament | Winning score | To par | Margin of victory | Runner(s)-up |
| --- | --- | --- | --- | --- | --- |
| 6 Jun 2010 | Memorial Tournament | 65-69-70-66=270 | −18 | 3 strokes | Rickie Fowler |
| 4 Jul 2010 | AT&T National | 69-64-67-70=270 | −10 | 1 stroke | Ryan Moore |
| 18 Sep 2011 | BMW Championship | 63-68-69-71=271 | −13 | 2 strokes | John Senden |
| 11 Mar 2012 | WGC-Cadillac Championship | 69-64-69-70=272 | −16 | 1 stroke | Bubba Watson |
| 16 Jun 2013 | U.S. Open | 71-69-71-70=281 | +1 | 2 strokes | Jason Day , Phil Mickelson |
Question:
When John Senden was the runner-up, what was the To Par?
Answer:
−13