Tan Kin Lian <10%
Tan Jee Say ~20-30%
Tan Cheng Bock ~20-30%
Tony Tan ~30-40%
I'm on a political fact-finding mission overseas now and don't have time to check the Constitution to confirm if there will be a run-off between the top two candidates, should the highest-polling candidate fail to secure an outright majority.
If so, then Tan Cheng Bock could conceivably win a second-round as the "opposition" sympathisers will have no other choice. If not, Dr Tony Tan will likely be the first president voted into office with less than an absolute majority.