Fresh from their first league win of the season seven days earlier, Argyle found themselves 3-0 up against their lower league rivals after just 23 minutes.
Lily Greenslade fired them ahead in the 18th minute before she added a second with a header three minutes later.
It got better for the Pilgrims two minutes later when St Austell scored an own goal under pressure.
The score remained 3-0 until half-time but the Green took only two minutes of the second period to increase their lead with a goal from substitute Beth Ireland.
St Austell pulled one back with a deflected shot, but Argyle added a fifth through Charlotte Whitmore in the 59th minute.
Greenslade had the chance to score a hat-trick when she was brought down in the box in the 65th minute but the goalkeeper saved her penalty.
Meanwhile Argyle’s under-23s beat Hashtag United Reserved 2-1 thanks to goals from Rose Mason-White and Ferne Orchard to progress in the FAWNL Reserves Cup.
In the South West Women’s League Premier Division, Liskeard Athletic were beaten 2-0 away at Shebourne Town.
In the South West Western League, Marine Academy Plymouth claimed a 9-2 home win over Budleigh Salterton.
The first half was tight, with Marine just edging it 2-1 with a goal just before the break by captain Samantha Drewery.
After that the floodgates opened for Marine Academy and goals followed at regular intervals.
Drewery pulled the strings for Marine and finished the day with five goals. Beth Overton, who has returned to the club, bagged a hat-trick, while Meg Boulton also got on the scoresheet.
In the same division, Saltash United overcame Sticker 5-4 away.
The Ashes had gone 4-1 by half-time but Sticker came back in the second period, however, the visitors did just enough to claim the three points.
Ella Stevens, Rachel Finch, Jade Chanel, Hayley Ranachan and Yazmin Franklin scored for Saltash, with Tori Marks (2), Gracie Davies and an own goal accounting for Sticker’s tally.
In the Devon Women’s League South & West Division, Lakeside Athletic got off the mark with an impressive 11-1 away with at Paignton Villa. Roxanne Byrne netted four times for Lakeside, with Rebekah Rose bagging a hat-trick. There were two goals for Toni Lunt, while Lauren Hewings and Jade Witt were also on the scoresheet.
There was a good derby game at Weston Mill, where SB Oak Villa edged out Signal Box Ladies 3-2.
Newcomers Hunters District had another tough afternoon, losing 30-0 away at Juventus Devon BiancanerA.
In the Cornwall Women’s League Division One, Saltash Borough started their season with a narrow 3-2 home defeat to Bodmin.
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