Villarreal are in Prague preparing to take on Sparta, defending a second leg 2-1 lead. If not for that away goal I think everyone would feel quite comfortable about progressing, but in spite of that 2-1 not being a fair reflection of the gulf between the sides, progression to the semis is far from assured.
The key here is for Villarreal to grab the first goal; do that, and probably Sparta's shoulders will drop. But if the home side gets the first goal, then the Submarine will have to score at least one goal to progress. Good news for the Submarine is Jonathan dos Santos returned and got some valuable time in on Sunday against Getafe, though Bonera and Musacchio are still out. And, Sparta Prague are struggling with injuries and suspensions at the back--Brabec and Nhamoinesu are suspended, Holek is doubtful (left the first leg against us with an injury and didn't play at the weekend).
Villarreal haven't posted an away win in awhile in the EL (not since Minsk in November), but they've drawn their last three matches on the road. Given Sparta's defensive struggles, I'm thinking a 2-1 win for the Submarine here.