  Let $Z$ be an $n$-dimensional Gaussian vector and let $f: \mathbb R^n \to
\mathbb R$ be a convex function. We show that: $$\mathbb P \left( f(Z) \leq
\mathbb E f(Z) -t\sqrt{ {\rm Var} f(Z)} \right) \leq \exp(-ct^2),$$ for all
$t>1$, where $c>0$ is an absolute constant. As an application we derive
variance-sensitive small ball probabilities for Gaussian processes.
