A healthy crowd turned up at Gaywood Park to watch a fascinating battle between two teams battling it out for fifth place.
Argyle were left with a mountain to climb after Watford took a 3-0 lead but the visitors, as they have done so often this season, showed courage, desire and commitment to make a game of it.
Pilgrims joint manager Dave Leonard was disappointed with the result but felt the team should still be proud of their sixth-placed finish in their first season back in the league.
He said: “I cannot blame the girls for their effort, commitment and desire against a team who were playing at a higher level last season.
“Once again individual errors let us down, but we know what we have to address in the off-season and we will go on from there.
“To finish in our highest ever position at this level is something the girls should be proud of. We know now we can compete at this level.”
Argyle went into the game without star striker Natasha Knapman, who was unavailable. That allowed Cornish teenager Nicola Champion to make her first league start. Zoe Cunningham returned from a two-match suspension to take her place on the bench alongside Ebony Dover and Darcey Hepworth.
Argyle got off to the worst possible starts when in the eighth minute Watford broke and Adekite Fatuga-Dada found the corner of the net.
This goal stunned Argyle with Watford’s international Helen Ward having an effort saved by Sarah Prior and Leanne Bell shooting wide.
Two minutes later Argyle’s Jessica Jones forced Weronika Baranowska into making a good save.
The Pilgrims began to come more into the game with young Champion holding the ball up well.
Greens captain Kate Middleton fired over the crossbar, before Watford’s Jennifer Kikomeko did the same at the other end.
Jones began to dominate the midfield and her pass to Kayley Lane saw her effort deflected into the arms of Baranowska. Jones then found Helen Bleazard, who headed wide.
But the Pilgrims were then stung when three minutes before half-time when O’Leary out-muscled a defender to make it 2-0.
Argyle started the second half on the attack with Baranowska saving from Bleazard at the near post and Steph Beck then firing over the Watford crossbar.
But the Pilgrims were left with a mountain to climb when Alysha Stojko-Down scored at the near post to make 3-0.
The visitors dug deep and Middleton had a fierce free-kick charged down and Mollie Taylor fired narrowly over the crossbar.
Finally in the 72nd minutes Argyle got the goal they deserved when Bleazard converted from a free-kick.
Two minutes after that Jones worked herself some space but was denied by a last-ditch Hatti Kettle tackle, while at the other end Prior had to be alert to deny Andrea Carid Cao.
Argyle continued to push for goals and it was game on when with seven minutes to play Bleazard cut the ball back to Cunningham, who fired home from just inside the penalty area.
Both teams battled for the next goal which never came.
Argyle: Sarah Prior, Leah Burridge, Faye Ivall (Darcey Hepworth 70), Kate Middleton, Mollie Taylor, Helen Bleazard, Steph Beck (Ebony Dover 80), Kayley Lane, Jessica Jones, Amber Pollock, Nicola Champion (Zoe Cunningham 75).