Alexa Coyle at the double as Hibs cruise through in Scottish Cup
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The Saints, managed by for former Hibs boss Grant Scott, ran out of steam in their clash at the Riverside Stadium.
Michaela McAlonie got the visitors off to the perfect start with the opener in the sixth minute before the SWPL 2 hosts drew level five minutes later.
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Hide AdBut a brace from American striker Alexa Coyle had Hibs in command at the break before further efforts from Shannon McGregor, Rosie Livingstone and Ellis Notley rounded off a comfortable afternoon in Perth for Dean Gibson's side.
Hibs will now host Gartcairn in the fourth round next month.
Meanwhile in SWPL 1, Spartans were beaten 3-0 by Motherwell who had former Ainslie Park midfielder Kaela McDonald-Nguah sent off.
Hearts put up a brave effort but lost out 2-0 to Glasgow City and in SWPL 2, Boroughmuir Thistle won 3-2 at Stirling University.