It continued the 28-year-old’s excellent run, which has seen him contribute three goals and four assists in the last six games.
Rigg was the beneficiary at Underhill, running on to Constable’s pass and sweeping in a finish to score United’s second goal.
He said: “Fortunately, James put a great ball through for me, it was perfect.
“I just had to take a quick touch and hit the target.
“James has been on fire ever since he scored his first goal of the season.
“He has a big impact on the team, he’s a handful and hopefully he can keep his form up and produce for the boys.”
Constable was delighted to play a key role and said the assist gave him as much pleasure as the goal.
“I’ve always enjoyed creating goals for other people,” he said.
“As a striker you want to be scoring, but when you have already got one it’s nice to put it on for other people. “Riggy had a great first touch and an even better second.”
Constable’s goal reminded him of his effort away to Swindon Town last season and thanked Michael Raynes for his unseen role.
He said: “It was a carbon copy of Swindon, it was nice to see Levs (Peter Leven) putting the ball in and Raynesy did me a trick by blocking my man and giving me a bit of time to get a header in.
“It was nice we got that bit of luck that perhaps we haven’t had in the last few weeks.”