"We are delighted to have got a clean sheet and progressed to the next round," Clough told the League One club's official website.
"We told the players we needed drastic improvements after poor performances at Colchester and Swindon and apart from a couple of late efforts we limited a very good Orient side to very, very few opportunities.
"This is the benchmark of how we want to defend. Tackles were going and blocks were being made. Regardless of what we do going forward, that is how we need to defend on a consistent basis."
United are back in League One action on Saturday when they welcome Gillingham to Bramall Lane.