Jack Sock has a new perspective about life on the tennis court after his brother had a narrow escape from a life-threatening illness last year.

Sock, who will face David Ferrer in the ASB Classic semifinals tomorrow, is coming off a career-best year in 2015, where he won his first ATP title and reached No26 in the world.

Sock - who is known for his charismatic on court persona - says his success is down to a reality check after his older brother, Eric, was hospitalised with a rare illness last January.

"With my brother being in hospital it made me take a step back ... it gave me a new perspective on life in general," said Sock. "They said my brother was 24 hours away from not making it and it really opened my eyes. I realised that tennis is my career and I love playing but there are other things in life."

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Eric Sock, who played high school tennis alongside Jack, was rushed to hospital after complications from pneumonia.

He was diagnosed with Lemierre's Syndrome, a rare (sometimes fatal) bacterial infection that was attacking his liver, kidney and heart. Eric was on life support for eight days - and Sock who was at home due to an injury - was by his side.

After that Sock has found a new tennis groove, lifting the trophy in Houston last year, reaching another final in Stockholm and compiling a 35-18 win loss record for the year.

He showed his powers of recovery today, coming back from an awful start to trump world No12 Kevin Anderson 1-6, 6-4, 6-4 in 98 minutes.

"He came out firing, didn't miss many first serves," reflected Sock. "From the ground he was playing really well but I was able to get a rhythm at the end."

The 23-year-old also showed his lighter side on court, tossing one of his socks to a surprised fan at the end of a match, a gesture he hopes might become his trademark.

"I'm trying it out for a bit to see how people react," said Sock. "A few guys have their signature things. I thought with such a unique last name it might be something clever and fun."

But Sock will need to be all business tomorrow, looking for just his second win over a top 10 player in 16 attempts.

"I'll have to be the aggressor, dictating points," he said. "If not [Ferrer] is very good at getting balls back, and making a lot of balls."