The Pilgrims were 3-0 victors over Coalville Town - as Ian Culverhouse's side bounced back strongly following Saturday's heavy defeat to neighbours Lincoln City.
Leak headed a 22nd minute opener from a Martin Woods corner, with Knowles adding United's second two minutes later. Richards scored goal number three a minute from time after connecting with Keaton Ward's flag-kick.
United (4-1-2-1-2): Cameron Gregory (Jake Lovelace 62), Zak Mills (Trialist A 62), Michael Bostwick (Trialist B 62), Tom Leak, Brad Nicholson (Ryan Hand 62); Martin Woods (Jordan Richards 62); Tom Edge (Sam Essien 62), Keziah Martin (Keaton Ward 62); Sam McLintock; Kelsey Mooney (Oliver Wilson 62), Jimmy Knowles (Michael Gyasi 46).
Referee: Callum Parke.
Attendance: 302.
PIC: Chris Simpson.