Brisbane QLD, Australia, 4 January 2015 | AAP

She may be listed as Croatian but wildcard Aussie Ajla Tomljanovic has been promptly adopted by locals after a sensational upset win over ex-world No.1 Jelena Jankovic at the Brisbane International.

The 21-year-old Brisbane resident will win over plenty more fans in the coming weeks judging by her 7-6(6) 6-0 first round thumping of sixth seed and world No.15 Jankovic on Sunday.

The hard-hitting Tomljanovic overcame early resistance to finally roll over former US Open finalist Jankovic in one hour and 45 minutes.

World No.62 Tomljanovic must be listed Croatian at Women’s Tennis Association events until she officially gains Australian citizenship, expected to be in the coming months.

However, the ex-world No.4 junior has been recognised as Australian at Grand Slams under world body ITF since last August’s US Open and that’s what she’ll be at the Australian Open this month.

She was embraced by locals at her first “home” tournament on Sunday since moving to Brisbane just months ago on the advice of coach Dave Taylor, the man who helped steer Sam Stosur to 2011 US Open success.

“I tried not think about it too much, just try to stay in the moment and focus more about my game,” she said of the home support.

“Every now and then it kind of goes through my mind that I have that (support) on my side now – it feels really nice, I must say.”

She had to hold her nerve against the 29-year-old Jankovic from the outset, breaking straight back after dropping her serve in just the third game.

Jankovic broke again in the ninth game but Tomljanovic dug deep to force a tiebreak.

The crowd favourite then saved two set points and converted her first to take it 8-6, ending an epic 70-minute opening set.

Tomljanovic then showed no mercy in the second set, claiming it in just 35 minutes.

Tomljanovic was born in Croatia but left for Florida when her family relocated at the age of 12.

She opted to move to Brisbane after being told by Taylor – her coach since late 2013 – that it had the best training facilities.

Meanwhile, Stosur will play American Varvara Lepchenko in the opening round later on Sunday and a victory would pit her against either Australian Open runner-up Dominika Cibulkova or rising American Madison Keys.