Tennis wunderkind Nick Kyrgios has continued his captivating grand slam run with a straight-sets win to storm into the US Open third round at Flushing Meadows.

Kyrgios produced a serving masterclass to sweep past seasoned Italian Andreas Seppi 6-4 7-6 (7-2) 6-4 and soften the blow of fellow Australian Samantha Stosur’s shattering defeat earlier on Thursday.

The 19-year-old Wimbledon quarter-finalist jammed down 22 aces and didn’t drop serve once to book a showdown on Saturday with Spanish 14th seed Tommy Robredo, the man who stopped Roger Federer last year in New York.

But while Kyrgios is savouring another sweet victory in his phenomenal rise to stardom, Stosur departed Flushing Meadows shellshocked after suffering a second-round defeat.

The 2011 champion blew two match points in a gut-wrenching 3-6 6-3 7-6 (10-8) loss to unseeded Estonian Kaia Kanepi.

Stosur appeared in command but unravelled in the second set, falling behind 5-0, and, despite leading 4-1 in the third-set tiebreaker and then having match points, was never truly able to wrestle back control in another disappointing early exit.

The Queenslander bombed out in the opening round last year at Flushing Meadows, falling to 17-year-old world No.296 Victoria Duval.

“I’m just really disappointed right now,” she said.

“It’s one of those matches where you walk off and think `what just happened?’

“I got off to a good start, really lost my way in the second set but started to get it back.

“But in the third set, we’re both playing pretty decent at the same time and it becomes a real fight and to get to two match points and not win, it’s not easy to walk off court losing.”

Fellow Australian Casey Dellacqua earlier lived up to her newfound seeded status to reach the third round for the first time.

Dellacqua overcame a one-set deficit, some dubious umpiring and 40 unforced errors to defeat Chinese qualifier Qiang Wang 4-6 6-4 6-2 in a major breakthrough for the 29-year-old.

With her expected third-round opponent, Serbia eighth seed Ana Ivanovic, faltering, Dellacqua’s plucky win presented the West Australian with a big opportunity to make the last 16 at a major for the first time outside of Australia.

The free-swinging left-hander will play unseeded Karolina Pliskova on Saturday after the Czech upset Ivanovic 7-5 6-4 in their second-round contest on Thursday.

“I am not overly surprised she beat Ivanovic, to be honest,” Dellacqua said.

“I practiced with her the other day and she was playing great.

“In these conditions, I think having a big serve like that is massive and I am going to have to play really well in the next round to beat her.”

Seeded 29th after soaring 152 places up the world rankings in the past 12 months, Dellacqua had been favoured to make light work of Wang.

But she did anything but, losing the first set and struggling to make inroads on the world No.139’s serve until deep in the second set.

Dellacqua stood two games away from crashing out of the tournament until, out of nowhere, broke Wang from 30-0 down to snatch the second set.

It took two controversial line calls against her in the fourth game of the deciding set to wake Dellacqua from her slumber.

After smashing her racquet into the back fence in frustration, Dellacqua didn’t drop another game and wrapped up the match after one hour and 59 minutes.

“It probably made me switch on a bit,” Dellacqua said.

“It made me get a bit fired up, get a bit of energy going, get the feet going. It felt good.”