SYDNEY (Reuters) - John Isner limped out of the Sydney International on Wednesday with his Australian Open participation in doubt but the thing that frustrated him most about his last 16 defeat was the umpire checking how long he was taking to serve.

John Isner of U.S. reacts during his men's singles match against compatriot Ryan Harrison at the Sydney International tennis tournament January 9, 2013. REUTERS/Daniel Munoz

The ATP are strictly enforcing a new rule giving players 25 seconds to get their serve away this year in a bid to speed up the game and big-serving Isner was a victim of the policy in his 6-4 6-4 loss to fellow American Ryan Harrison.

"I knew about the rule, but I went on the court and wasn't really thinking. I had it called right way my second service game, I think," he told reporters.

"For someone who sweats a lot like me, that's why I wear a hat, because I can't play without a hat. It's always dripping. I felt like I could never go to the towel. The umpire was looking at me the whole match.

"When I got called on the warning I was getting ready to serve. I was at the line. I don't particularly like that rule, that's for sure, because it messed with my rhythm, my flow, and I'm sure it's doing that to a lot of other players, too."

Isner, however, does not think it will be a problem at Melbourne Park next week.

Although grand slams have a shorter time limit of 20 seconds, the rule is not enforced and the likes of Novak Djokovic and Rafa Nadal are notorious for their long build up to serving.

The new ATP rule calls for a warning followed by the loss of a point for the offending player.

It was endorsed by the player's council last December but Isner, who is suffering from a bone bruise to his right leg, thinks they should boost the time up to 30 seconds.

"Every time I'd look up he's doing this," Isner added of the umpire, gesturing as if starting a stopwatch.

"It throws you off. I'm not intentionally trying to stall out there, but I've always moved a little slower. You know, at certain points in the match you need to take five extra seconds.

"I have to go to the towel to wipe off sweat that's dripping off my hat. I really felt like I wasn't able to do that, so I don't like this rule.

"If they did keep it as something new I would have to adjust, for sure. I don't like it. I feel like majority of players ‑ maybe not the majority. I think most players would be on my side, I think. I could be wrong."

(Editing by John O'Brien)

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