Kai seals US semi spot
© AFP

Substitute Natasha Kai emerged as USA's extra-time heroine, heading home a dramatic winner to settle a memorable North American derby and set up a semi-final date with either China PR or Japan.

The drama traditionally associated with this fierce cross-border rivalry had been cranked up a notch when, with just 19 minutes played, a ferocious lightning storm forced the referee to call a temporary halt to proceedings.

Complicating matters further was the fact that, by this point, the US had already raced into an early lead, Angela Hucles firing home from close range on 12 minutes after Heather O'Reilly's initial header had been parried clear by Erin McLeod.

Yet whatever Canada's Norwegian coach Even Pellerud said to his players during the unexpected, hour-and-40-minute break, it certainly seemed to do the trick as they re-emerged from the dressing rooms with a renewed sense of purpose to their play.

It was improvement that, within ten minutes, was rewarded with an equaliser that summed up the Canucks' transformation. True, the US did not aid their own cause with a botched clearance, but the speed with which Canada punished them left much to admire, Clare Rustad spraying a square pass for the onrushing Christine Sinclair to smash the ball past Hope Solo.

Their advantage eliminated, USA attempted to respond immediately, with Hucles passing up a glorious opportunity to restore their lead within seconds. The 30-year-old midfielder looked to have done the hardest part in timing her run to latch on to a long cross-field pass while remaining onside, but although it appeared inevitable that she would go on to double her tally, Hucles instead dragged her shot wide of the far post.

Undeterred, the Americans went on to dominate the second half, with Shannon Boxx - playing her 100th senior international - heading narrowly wide after 65 minutes and Hucles forcing a fine save from substitute goalkeeper Karina Le Blanc six minutes later.

Canada remained dangerous on the break, however, and Sinclair might have won it for them with 12 minutes remaining but for a superb save from Solo that kept out the striker's powerful long-range shot.

USA remained the more determined attacking force as the match entered extra time and, with Canada seemingly eyeing penalties, the fatal blow was struck. With 100 minutes showing on the clock and the Canucks retreating further back into their own half, Boxx curled over a tantalising cross that Kai diverted expertly past the helpless Le Blanc.

Pellerud's side simply had no answer, nor could they have any complaints about a result that leaves their old rivals to face Japan in the last four.