Tennis: American star Jack Sock takes up unusual role at ASB Classic

American tennis star Jack Sock had an unusual role at the ASB Classic on Tuesday, taking the role of umpire for a charity tennis match.

World No 23 Sock was in the chair for a match between representatives from two Auckland clubs, who were playing for a gold leaf Moet and Chandon Jeroboam valued at $20,000.

Sock enjoyed the experience, overseeing his first match from the chair since his days as a junior.

"It was fun," said Sock. "To see a couple of guys come out and play for a pretty sweet prize - they said it was worth $20,000 - there was a lot on the line there. Last week at the Hopman Cup when I challenged a call I got up in the chair but before that it's been a while, probably since I was very young."

Sock has become famed for his sense of fair play, and twice in the last 18 months he has conceded a call in favour of his opponent, against Australian Lleyton Hewitt and Frenchman Richard Gasquet.

"We get calls all year," said Sock. "Some go against you [and] some go for you. [But] when it is as blatant as that one [against Hewitt] and in the game against Richard sometimes you let it go and give it to them and move on."

The 24-year-old has also learnt not to remonstrate with umpires, regardless of how frustrated he might be during a match.

"You can get all upset about it but most of the time it will be worse for your play," said Sock. "If you look at the top guys no one really says much...it's better to let them go by."

There was no such drama on Wednesday, though it was a surprisingly competitive match between representatives from the West End and Gladstone tennis clubs.

Westend's Mark Osbourne prevailed in the end, over Gladstone club president Geoff Hosking.

"It was a great experience," said Osbourne. "When I got called to see if I was available I jumped at the chance. I go to the tennis every year so to be playing in front of Jack Sock was awesome."

"[But] I was very nervous this morning when I realised that this Jeroboam is worth $20,000 because I didn't want to let our club down. Thankfully it all turned out well."

The Westend Club have just completed a rebuild but Osbourne said there was a "bit of a shortfall" so the proceeds from the auction of the Jeroboam will be "well used."

Sock faces compatriot Ryan Harrison on Wednesday in the second round, with other top seeds David Ferrer and John Isner also in action.