He stated in a post fight interview that his right left him off balance after throwing in, which was why he only wanted to use it when he was pretty sure it would land.

edit:

Afterwards the victorious Ukrainian said he didn't want to risk throwing his right more and missing.
"I had to make sure I would land them," said Klitschko. "If I would miss I would lose the balance and it's hard to get back.
"I thought I was going to knock this guy out - it wasn't easy. I know you're not satisfied, but I have to keep the belts and knock everybody else out."



quote from the BBC