Leigh, just 16, was outstanding alongside Rodrigo Defendi, only 18, as the Rams knocked, knocked and knocked again but couldn't break through at Pride Park.
Always lively on the counter ourselves in an entertaining second half, Jamie Slabber's goal was enough for a 1-0 win.
That win was the reserves' sixth on the trot and eighth in nine games and took them to the top of the Barclays Premier Reserve League South this week.
"Leigh was nervous before the game, which you like to see and I thought he was absolutely excellent," said Clive.
"He was playing against Marcus Tudgay who has played in the Championship and I thought it was going to be a real test for him. He came through that test with flying colours.
"The good thing about Leigh is that he's willing to learn, listens and with Rodrigo, the pair of them were outstanding.
"What people have to undertsand is that it's Leigh's first year, he's training full time and there are a lot of demands on the lads.
"It's not easy to adjust to the physical pressure or the mental pressure because they all want to do well but he showed he's capable of that and for one so young, that's very impressive."
Clive Allen couldn't speak highly enough of young defender Leigh Mills after his superb full debut for the reserves against Derby County on Tuesday night.