SCOTUS held that a petition for certiorari is not part of the state post-conviction proceeding and thus a petition for cert does not toll the 1-year statute of limitations. According to Justice Thomas:
This Court is not a part of a "State's post-conviction procedures." State review ends when the state courts have finally resolved an application for state post conviction relief. After the State's highest court has issued its mandate or denied review, no other state avenues for relief remain open. And an application for state post conviction review no longer exists. All that remains is a separate certiorari petition pending before a federal court.