The Blues manager reacted to a disappointing first-half showing by introducing both players at the break and it proved an inspired decision as Thomas bagged a brace and Redmond got his first of the season to seal a pivotal 3-1 comeback win.
Explaining his decision to take the unusual step of bringing on two subs at the interval, when his side were trailing 1-0, Clark said: "Even though there wasn't too much in the first-half I just felt that Derby were gaining momentum by each minute and the game was there to be taken if we wanted to. All week I've talked about the young, hungry players that Derby have and we had to match that to get anything from the game, but we didn't and they were more energetic than us in the first-half. I decided to get the two lads on with a bit of power and pace and it caused them problems. I'm delighted for the pair of them."
Referring specifically to Redmond, he continued: "Nathan has waited a long time for that first goal of the season but it was a fantastic goal. He earned a lot of plaudits early in his career but with young players their form can be a bit up and down. I hope that'll give him the confidence because I certainly believe there's a double-figures goal-scorer in there, even playing from a wide position. He is technically very good, he's lightening quick and defenders hate that.
And on Thomas, the boss revealed: "I had a chat with Wes on Thursday just to say my belief in him was still there. There was a lot of pressure on him and he's desperate to do well because he wants to stay at this football club beyond this loan period. And he's shown me today what I'd seen of him in the past in his time at Bournemouth, Portsmouth and Blackpool. He scored two, his hold-up play was good and his work-ethic is fantastic. We just played with lots more power, pace and energy and we did to Derby in the second-half what they'd done to us in the first-half."
Clark was also eager to praise the performance of another of his loanees, Newcastle man Shane Ferguson, who filled in a left-back in the absence of Mitch Hancox. "I've just got to say, even in the first-half when we hadn't been so good, I thought Ferguson was outstanding from start to finish," added Clark.
The victory moved Blues up to 14th in the table, opening up a seven-point buffer between themselves and the bottom three. Clark admitted: "We just needed to win. It was massive for us. We'd done enough on Tuesday (against Blackpool) to get the three points but it just didn't happen. But I'm delighted with our second-half performance today."