How in the world???
3. c5 is a pretty bad move, and after it, Black is probably a bit better than equal, as long as he challenges White's premature push with ...b6! (either immediately or after something like 3. ...Nf6 4. Nf3 b6!
You may as well play it immediately - 3. ...b6, and White has nothing better than to take. After 4. cxb6 axb6, White's early attempt to gain space has backfired - Black's Rook is happy with its new open a-file, the c8 Bishop has a way to get into the game, and the b6 Pawn supports a later ...c5 break by Black. Note that if White tries to maintain his Pawn on c5 with 4. b4, Black plays 4. ...a5 and White's getting into trouble because he can't keep the chain intact - after 5. a3 axb4, he can't take back because of the pin on the a-file. And after 5. b5 bxc5, White's losing a Pawn.
It's worth remembering this pattern, because this is often how to react to this kind of push. It's similar to the way White plays if Black takes the Queen's Gambit Pawn and tries to hang on to it.
Hope this was some help!
Queens Gambit Declined-
How do you deal with the pawn push C4 to C5 in this opening?
My friend does this to me and it traps in my dark-square Bishop and limits Black's movements in the game. He can always support c5 with b4.
1. D4 D5
2. C4 E6
3. C5