Ouch. I think the best outcome I can attain is to lose 15-14.
1. mathgrant wins 13-12.
2. mathgrant wins 15-15.
3. mathgrant wins 13-13.
4. Selden wins 15-14.
5. mathgrant(X) vs Selden(O), board diagonals2
6. Selden(X) vs mathgrant(O), board diagonals2
7. Selden(X) vs mathgrant(O), random board