Tomic into Australian Open junior semis

Sara Tomic is two wins away from completing a rare family double act at the Australian Open.

The younger sister of Bernard, Tomic once again showcased her fighting qualities to beat fellow Australian Baijing Lin 6-1 5-7 6-2 on Thursday and reach the semi-finals of the girls' championship at Melbourne Park.

The 17-year-old battled a stomach complaint and recovered from a service break down in the second set to move into the last four in her fifth and final Open junior tilt.

"I'm always surprising myself," Tomic said.

"Honestly, I didn't even tell my team that I wasn't really feeling good. My stomach was hurting.

"I had to take some tablets after, and mentally I wasn't focusing.

"(But) I'm really hungry for winning and I truly want to do well and always do my best on the court."

A newfound focus on her fitness and movement paid dividends as Tomic hit a series of impressive winners on the run to save four break points in a key game in the deciding set.

"I've been improving my weaknesses, which is getting to the ball," Tomic said.

"So now I can actually run to the ball and I feel like my defence has definitely improved."

Older brother Bernard - now the men's world No.17 - won the Australian Open boys' title at 15 in 2008 and then the US Open junior championship in 2009.

If Sara can triumph in Melbourne this weekend, the Tomics would become the first Australian sister-brother duo since Lorraine Coghlan (1956) and Will Coghlan (1960) to win the Australian junior singles championships.

"I'm trying to win. It'd be nice," Sara said.

"It'd really be a dream to be on the board."

Fellow Australian Alex De Minaur could also follow in Bernard's footsteps after sealing a spot in the boys' semi-finals.

A semi-finalist also in last year's US Open junior singles, De Minaur ousted Greek third seed Stefanos Tsitsipas 6-7 (3-7) 7-5 6-0 on Thursday.

Oliver Anderson also advanced with a 3-6 6-4 6-4 victory over Max Purcell, giving Australia two of the four berths in the boys' semis.