But the game was overshadowed by a serious injury to Nicholls which resulted in Vale skipper John McCombe being dismissed.
Cobblers started brightly, Anthony Charles and Kelvin Langmead went close before Nicholls gave Cobblers a 20th minute lead. But it came at a heavy price with the club's top scorer receiving a suspected broken leg.
Nicholls latched on to a short back pass from Robert Taylor to go around goalkeeper Chris Neal and slip the ball into an empty net but he was challenged by McCombe in doing so. The Vale skipper was sent off and Nicholls taken from the pitch in an ambulance following a long hold-up.
Moult should have doubled Northampton's advantage moments after coming on for Nicholls when he headed straight at Neal. But Moult made no mistake in the 42nd minute, racing on to Adebayo Akinfenwa's neat pass to slip the ball under Neal.
Akinfenwa should have increased Northampton's lead immediately after the restart but he headed wide with the goal at his mercy. Ashley Vincent almost reduced the arrears when he broke away only to be denied by Lee Nicholls.