Stevens fired in on the stroke of half-time to give Poppies the lead before Arel Amu levelled from the spot with 52 minutes on the clock.
The status quo remained for 20 minutes before Stevens found the net again to give his side three points to keep them firmly in the Evo-Stik South Premier play-off picture.
Corby Town scored twice in the second half as they fought back from a goal down to beat Chasetown 2-1.
Jake Bettles got both goals - on 64 and 80 minutes - to maintain the Steelmen's outside hopes of forcing their way into the top six.
AFC Rushden & Diamonds dropped points in their attempts to wrap up the Evo-Stik South East title.
They needed a second-half goal from Joel Gyasi to earn themselves a point away to 17th-placed Northwood.