Nadal, in 3 consecutive meetings with James Blake, had lower success on 1st serve than on second. Never happened to Blake in their series.
2006 Masters Cup (lost to Blake)
Nadal - 50% on 1st, 54% on 2nd
2008 Indian Wells (d. Blake)
Nadal - 62% on 1st, 69% on 2nd
2008 Miami (d. Blake)
Nadal - 65% on 1st, 84% on 2nd
In that last match Nadal lost only 3 of 19 points on 2nd serve