Aussie young gun fires 100m warning shot

After firing a warning shot, Australian young gun Kyle Chalmers now has history in his sights at the Rio Olympic pool.

The 18-year-old upstaged world No.1 and teammate Cameron McEvoy to be second fastest in the 100m freestyle semi-finals on Tuesday night.

He trailed only the man who denied Australia 100m gold at London - American Nathan Adrian.

Few would rule out McEvoy as a chance to become the first Australian to claim the 100m Olympic title since Michael Wenden in 1968.

But few have seen anything quite like Chalmers before, either.

After setting a junior world record to be fastest in the heats, Chalmers backed up hours later to shatter the mark again by clocking 47.88 seconds.

The time would have won silver at the 2015 world titles in Russia.

Defending champion Adrian bounced back from an ordinary heat that almost cost him a semi-final spot by topping the timesheets in 47.83.

McEvoy was third fastest in 47.93.

In a repeat of his heat, Chalmers was well behind at the 50m turn but again flicked the switch to win his semi-final comfortably.

"That's how I swim. I swim to my strengths, and my strength is my back end," Chalmers said.

"But I probably didn't expect to get through to the final, especially in that time."

Plenty of pressure will now be on Chalmers and McEvoy to end Australia's 100m drought at the Olympics.

Something Eamon Sullivan and James Magnussen could not do despite entering the last two Olympics as red hot favourites respectively.

But instead of dreaming of history, the mild mannered Chalmers simply wanted a good night's sleep.

Asked about his chances, Chalmers said: "I am probably trying to wind down, block it out of my mind completely, otherwise I will be up all night."

McEvoy arrived at Rio as the red hot favourite after clocking 47.04 at April's Rio trials - the third fastest of all time and quickest outside a supersuit.

But Chalmers' blistering speed at his first Olympics has ensured the form guide will be thrown out the window in Wednesday night's final.

At least McEvoy won't have to worry about the man who denied him 2015 world titles 100m gold.

China's Ning Zetao (12th, 48.37) failed to make the final.