Canada fight back to end Ireland's World Cup dreams
The pressure was on Olympic champions Canada after being held to a goalless draw against Nigeria but they fought back in Perth after the worst start possible.
They were left stunned in the fourth minute when Arsenal midfielder Katie McCabe scored direct from a corner, much to the delight of the 17,065 fans, most of whom were loudly cheering for Ireland despite the rain.
But Canada clawed back through an own goal from Megan Connolly just before half-time before Leon provided the winner in the 53rd minute.
The result ended Ireland's hopes of progressing on their World Cup debut.
Canada moved top of Group B with four points, ahead of Australia's clash with Nigeria in Brisbane on Thursday.
They received a boost with Chelsea midfielder Jessie Fleming returning from a calf injury and she took the captain's armband from Christine Sinclair, who only started on the bench.
Evelyne Viens was preferred in attack after sparking Canada as a substitute against Nigeria.
Ireland were forced into a late change when Florida State forward Heather Payne suffered a hamstring injury during the warm-up and was replaced by Aine O'Gorman.
With their tournament hopes on the line, an aggressive Ireland ran Canada ragged in a spirited start.
They had goalkeeper Kailen Sheridan scrambling in the third minute when a cross from Lucy Quinn was almost met by Kyra Carusa.
But McCabe scored on the subsequent corner with her vicious left-foot in-swinger bamboozling Sheridan, whose outstretched fingers only managed to deflect the ball onto the right post and into the net.
McCabe had tried something similar against Australia without success in their 1-0 opening defeat, but after spotting Sheridan slightly off her line she made no mistake this time.
Canada attempted to stymie Ireland's momentum by playing a possession game, but struggled to penetrate Ireland's gritty defence led by Louise Quinn, who took her place after overcoming a foot injury sustained against Australia.
Canada had their first clear opportunity on the half hour, but Vanessa Gilles missed from close range after being on the end of a clever flick from Kadeisha Buchanan.
As the rain cascaded onto the ground, Canada's persistance was rewarded just before half-time when a cross from Julia Grosso on the left side snaked through the Irish defence and deflected off Connolly for an own goal.
Canada coach Bev Priestman made three changes to start the second-half, including bringing on Sinclair.
It seemingly did the trick with Canada playing with more intent as they peppered the Irish goal.
Canada went ahead when a superb through ball from Sophie Schmidt found Leon, who fired past goalkeeper Courtney Brosnan.