Jack Sock almost didn't play the Auckland semifinals because of an illness, but wound up getting one of his biggest wins.

Sock defeated four-time Auckland champion David Ferrer and will now play his second tour final, assuming he is fit enough to take the court.

"I knew coming in I would have to play some unbelievable tennis,” he said following the semifinals. “It was a difficult day. I woke up with some flu-like symptoms. I didn’t know if I was going to play."

Instead, he played "some of the best tennis of my career" in defeating the top seed in three sets.

"Maybe I can stay sick through Melbourne and play like this," he said.

Sock won his first tour final in Houston in 2015.