By Simon Fudge
Last Updated: 01/01/70 1:00am
After a 0-0 first half, debutant Paul Simpson put the home side in front nine minutes after the break.
However, The Pilgrims equalised through substitute Marino Keith on 65 minutes and with ten minutes to go, Graham Coughlan made it 2-1.
Lee Hodges scored a third with six minutes remaining to book Argyle's promotion for next season and take them five points clear of Luton Town, at the top of Division Three.
Cheltenham Town moved into fourth with a 2-1 victory over Kidderminster Harriers at Whaddon Road.
Colin Larkin gave Kidderminster a 1-0 lead before Tony Naylor equalised for The Robins five minutes before half-time.
Nathan Tyson took the points for Cheltenham, when he scored the winner with 14 minutes to go.
Steve Cotterill's side moved to within two points of third-place Mansfield Town and sight of automatic promotion, with a match in hand on The Stags.
Kidderminster stay four points adrift of the promotion play-off places in tenth.
At the other end of the table, struggling York City moved up three places to fifth from bottom, with a 2-0 win over Lincoln City at Bootham Crescent.
Lee Bullock scored in the first minute and Lee Nogan made made it 2-0 nine minutes before half-time to seal the points.
The Imps never had a reply to the two-goal deficit and they drop dangerously close to the bottom of the Division Three table, lying ten points above bottom club Halifax Town.
Click here for an updated Division Three table