Brisbane QLD, Australia, 5 January 2015 | AAP

Once a “short, fat kid”, Australian teenager Thanasi Kokkinakis has shown he is ready to come of age in 2015 with a stunning Brisbane International first round upset on Monday.

And fellow Australian wildcard – James Duckworth – also appears poised to make a name for himself following his own boilover.

World No.149 Kokkinakis, 18, has set up a potential second round showdown with compatriot Bernard Tomic by downing French eighth seed Julien Benneteau 6-4 6-3.

And world No.125 Duckworth earlier blew away sixth seed Gilles Simon, also of France, 6-2 6-2 in just over an hour at Pat Rafter Arena.

Kokkinakis had a hard act to follow after Duckworth thrashed former world No.6 Simon, currently ranked 104 places higher than the NSW 22-year-old.

But Kokkinakis shrugged off an early break to find his swagger and show how far he had come in a year by clinching his first career win over a top 25 player.

Twelve months ago, Kokkinakis was the new kid on the block when he lined up against Hewitt in the Brisbane International first round via the qualifiers.

Now he is the next big thing along with fellow member of the “Special Ks” – Wimbledon quarterfinalist Nick Kyrgios – after breaking into the top 150 having started 2014 ranked No.570.

“I was short and fat as a kid,” Kokkinakis said dryly.

“But I have grown up and worked out the way I want to play.

“My start today was pretty average. I don’t train for that sort of rubbish but luckily I found my groove.”

In another indication of Kokkinakis’s rapid rise, the Adelaide youngster proved too strong for the Frenchman who downed him in a Davis Cup dead rubber early last year.

He showed no mercy to the world No.25 who appeared to be battling a hip complaint, prompting a seven minute first set medical time out.

Kokkinakis sealed the 74 minute match with his ninth ace.

Duckworth stole the early limelight on centre court in Brisbane doing his best Hewitt impersonation.

Wearing a cap backwards and with fists pumping, Duckworth proved too powerful for former Australian Open quarterfinalist Simon.

Duckworth is on track for a potential quarterfinal showdown with Roger Federer.

It was a remarkable win by Duckworth who failed to defeat a top 100 player last year.

Then again, Duckworth comes from reasonable tennis stock – his grandmother, Beryl Penrose, won the 1955 Australian Open singles and doubles.

“My goal is obviously to get inside that top 100 – hopefully I can push forward over the summer and get in the main draw of those grand slams,” Duckworth said.