Given the size of the forces involved, it is possible
Given the size of the forces involved, it is possible; the Mexican force numbered about 1500 (Santa Ana and Cos, combined) and the Texans numbered about 800, all by April 21.
However:
Santa Ana's 1100 had been awake all night, expecting an attack under cover of darkness, while Cos' 400 had marched overnight;
Houston's troops, although making a march of 60 miles in 2.5 days, had been at San Jacinto and in the woods since April 20;
The Mexicans were, literally, "caught napping" at about 4:30 pm; there are some sources that not only was the combined force not disposed for battle, they didn't even have pickets (the roots of Anaxgoras' "post sentries" comment) out;
The Texans demonstrated a better tactical ability, moving in silence before the final charge;
The Texans were in their own country, definitely had better morale and esprit d' corps, and had the Alamo and Goliad to inspire them;
The Mexicans were deep in relatively unfriendly territory, and knew Gaines' US force was moving west - they were still more than 300 miles away, but they were closer than significant reinforcements;
It was an infantry battle, but Texan artillery outnumbered Mexican by 2-1.