Two goals in the opening 12 minutes put Rushden on course for victory in the Northamptonshire derby at Kettering.
Craig Farrell got the visitors off to the perfect start with a close-range finish, before Mark Byrne converted Aaron O'Connor's cross for number two.
Top scorer Lee Tomlin put the result beyond doubt after the break with a low right-foot drive from 12 yards.
Jefferson Louis was denied a fourth by the bar, while James Dance wasted Kettering's best chance.
The result means Rushden remain fourth but have a 10-point cushion over the sixth-placed Poppies in the race for the play-offs.
Kettering manager Lee Harper said: "To find ourselves two down after ten or 12 minutes left us with a mountain to climb, but after 90 minutes they were the better team.
"They took their chances, and the boys' heads went down a little bit.
"We're gutted to have been well and truly beaten, and by our fiercest rivals. I changed things around tonight, and I'll go away and look at myself and ask myself whether I could have done anything differently."
Rushden manager Justin Edinbugh said: "I said before the game we didn't need to win this one, the emphasis was on Kettering, and I think that made it better for us.
"I thought we started brightly, like I asked, and exploited the space down the flanks.
"We seem to travel well, we find a lot more space and counter-attack very well. We did that tonight, and I was very pleased."
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