Kalvin Phillips made his first appearance since January for Leeds United in their match against Reading last weekend.
Phillips and Erwin have seen a lack of action at Elland Road recently, with both seemingly falling out of favour.
However, the pair played a part as Leeds managed to overturn a deficit to claim the three points against Reading last weekend.
And Evans said: “I’ve always said that if people produce performances in training we will promote them up. And the two lads that came on - in Lee and Kalvin - have worked hard in training.
“I was particularly pleased with young Kalvin today, I don’t think he expected to get on the bench, let alone get on the pitch.”
Erwin was brought to Leeds last summer, but he is yet to make much of an impact for the Yorkshire club.
The Scottish striker has had a difficult first year with the Whites, where he has found appearances hard to come by.
Erwin is yet to score for Leeds in 10 substitute appearances, and he also failed to hit the back of the net during a loan spell with Bury earlier in the campaign.
Phillips, meanwhile, has played 10 times this term, but he has failed to nail down a starting spot.
The 20-year-old is still regarded as one of the best prospects coming through at Leeds, but he will be eager to stake his claim for a regular first-team place over the final few weeks of the season.