Chris Brayford made three changes from the side that beat Spurs Reserves 5-0 last time out, with Latoya Smith, Cheryl Anderson and Egle Trezzi replacing Naomi Ogunde, Danielle Griffiths and Ellie Stenning.
This was the first time the O’s had reached the second-round of the F.A Cup and fired up by the occasion they broke the deadlock early on through Allison McCann. The American midfielder showed great composure to round the keeper and poke home, after being found in the box by Anderson.
In tough conditions at The PMC Stadium, the home side began to battle back. Rebecca Bath looked particularly lively for Pompey as she fired a couple of strikes just past the post in quick succession.
It was Bath who eventually did equalise for the hosts in the 28th minute with a low drive into the bottom corner.
Orient had a chance to regain their lead when Sophie Le Marchand picked out Hayley Barton in the box, but a last-ditch tackle prevented the O’s winger from pulling the trigger.
Five minutes later though, Portsmouth were ahead. Bath with an almost carbon copy of her equaliser, firing low and hard past Smith.
Tamsin De Bunsen then added a third for Pompey in the 38th minute. The forward slotting home from Hayley Bridge’s cross.
Just before half time, Smith appeared to be a bundled over in the box by a Portsmouth forward. However, the referee didn’t adjudge it as a foul on the O’s keeper, leaving Laura Ingram to tap into an empty net.
Brayford made a switch at half time which saw Otesha Charles make her return from injury, as she replaced Pinja Piira.
Charles almost made an instant impact, breaking through on goal, only to be denied by Hannah Haughton in the Pompey goal, who bravely dived in to prevent her getting a shot away.
In the 65th minute, De Bunsen added a second with a fine long-range strike from around 35 yards out, leaving Smith with no chance.
Immediately afterwards the O’s almost pulled one back when Ria Collins headed just over from Barton’s in-swinging corner.
Orient made another change shortly after, with Barton making way for Valeria Moreno.
Ten minutes later, Smith was at full stretch to produce a fantastic save to deny Bath her hat-trick.
Brayford made his final change five minutes from time, bringing on Demi Brown for Fran Ali, before Pompey added a sixth and final goal through Jazmin Younger.
Speaking after the tie, O’s vice-captain, Sophie Le Marchand, thought her side’s performance was a lot better than the result suggests.
Orient: Smith, Anderson, Collins, Bastyr, Piira (Charles 45”), Ali (Brown 85”), Trezzi, Barton (Moreno 68”), McCann, Auguste, Le Marchand
Goals: McCann 7”
Portsmouth: Haughton, Tonks, Ingram, Currie, McDonnell, Bradley, Rowe (Younger 85”), Bridge, True (Adaway 71”), de Bunsen (Southgate 85”), Bath
Goals: Bath 28”, 35”, De Bunsen 38”, 68”, Ingram 43”, Younger 87”