AUCKLAND, New Zealand - Bianca Andreescu isn't done making her mark on the ASB Classic: the teenage qualifier knocked off her second consecutive big-name scalp to move into her maiden WTA Tour semifinal, coming from a set and a break down to defeat No.6 seed Venus Williams 6-7(1), 6-1, 6-3.

The 18-year-old had sent shockwaves through the tournament by eliminating top seed Caroline Wozniacki 6-4, 6-4 in the second round - and her multifaceted all-court talent was once again on display in backing that career-best win up.

Andreescu came out of the blocks looking to dominate - and over the course of the match managed to maintain a more aggressive game than Williams, one of the sport's legendary power players. But despite striking 15 winners to the American's two in the first set - including two clean return strikes - Andreescu struggled with her consistency and her serve, with 32 unforced errors and five double faults in the debit column.

Four service holds of superb quality were followed by four rather error-strewn breaks, before Williams snapped the pattern with some booming serves to move within a game of the set. Down 15-30, Andreescu came up with some brave backhands to stay alive, ultimately forcing a tiebreak - but once there, the young Canadian was unable to find any form, losing seven straight points, including five errors and a double fault, to fall behind by a set.

Continuing to hit wildly, Andreescu would immediately lose her serve to love at the start of the second set. But a subsequent epic four-deuce tussle on the Williams serve would prove to be a turning point. Showing off her point construction on both offence and defence, an Andreescu drive volley set up a fourth break point - and a canny low forehand pass followed by a heavy backhand pass would seal the break back.

From there, a rejuvenated Andreescu entered an astonishing purple patch in which everything she tried worked. Her rock-solid backhand piled relentless pressure on the seven-time Grand Slam champion, and her net play was impeccable. Crucially, too, Andreescu fixed her serve, raising her first serve percentage from 51% in the first set to 69% in the second and 65% in the third.

And although the World No.152 never backed down from her aggressive strategy, she was also able to show off some wonderful defence when forced: twice Andreescu slipped over but still won the point, and a running dropshot winner en route to breaking Williams for 5-1 in the second set was the shot of the match.

From a set and 0-1 down, Andreescu reeled off an eyebrow-raising 11 consecutive games to take her to the brink of victory: indeed, the teenager would win 20 of the first 28 points of the deciding set to move up 5-0, preventing her illustrious opponent from even reaching game point until the sixth game.

Williams has never made life easy for players trying to close her out, though, and even at this stage betrayed no sign that she was ready to accept defeat. Raising her aggression and accuracy, the 2015 champion snatched three games back on the trot, breaking Andreescu twice and raising the possibility of a spectacular comeback.

But serving to stay in the match at 3-5, Williams faltered again. A dead net cord was a much-needed stroke of luck for Andreescu, but the Canadian's forehand return winner - her 39th of the day - to reach three match points was not. Williams saved the first, but on the second Andreescu's dogged defence would come into play again. Scampering around the court, Williams eventually went for too much once again to commit her 46th unforced error - and Andreescu's fairytale run continues, with either No.3 seed Hsieh Su-Wei or Sara Sorribes Tormo up next.