From the way that horse run, I think that silence suzuka itself. He died during Tenno Sho after all.
The thing is, the real Silence Suzuka was a chestnut with a noticeable blaze, and the jockey's racing silk is not a match (ref). The general details fall more in line with Panthalassa, who's bay and has a racing color that is similar to what's depicted, but the green stripe on the sleeve for Pantha's racing silk is red here.
P.S. For a moment I thought it was Jack d'Or, as he too is a runner (as we can see from this year's Tenno Sho), but he too has a big blaze and the racing silk is not a match either...