Padraig Amond scored a hat-trick and took his tally of league goals for the season to 30 as Town climbed up to third with victory at Woking.
Amond fired the visitors ahead after being teed up by Andy Monkhouse.
Woking's Cameron Norman saw his free-kick crash against a post before Amond netted his second following good work from Omar Bogle and Craig Disley.
Bruno Andrade slotted home from close range to pull a goal back, but Amond sealed the points with a cool finish.
The Mariners, who were beaten in last season's play-off final, needed two points from the remaining two games to secure a top-five spot this term.
1 McKeown, 2 Tait, 22 Nsiala, 31 Nolan, 32 Horwood, 8 Disley, 23 East, 6 Gowling,
10 Amond, 11 Monkhouse, 9 Bogle.