To run out of steam means to lose momentum and fail, but in this context he could sustain his energy and not fail if the match goes to five sets.
Context: "It could be a long match tomorrow, and he could sustain his energy and not fail if it goes to five sets."
Hypothesis: It could be a long match tomorrow, and he could run out of steam if it goes to five sets.
Based on the context, is the hypothesis true, false, or unknown?