Ranked 82nd in the world, Pironkova dumped five-times champion Williams out of the tournament 6-2 6-3, to become the first Bulgarian woman to reach a grand slam semi in the open era.
Not bad for someone without a grass court in her homeland and a grand slam record that until now had not stretched beyond the second round.
The 22-year-old graced a media frenzy once before having shocked Venus in the Australian Open in 2006, only to lose in the next round. Now she must master the limelight as well as 2009 Australian Open semi-finalist, Zvonareva.
The Russian, seeded 21, came up with a shock of her own to make the last four of Wimbledon with victory in over U.S. Open champion Kim Clijsters.
She is also enjoying a Wimbledon best, having previously never gone beyond the fourth round at the All England Club.
Zvonareva and Pironkova have met once before, last year in Moscow with the Bulgarian sauntering to victory 6-0 6-2.
"You know, it's hard to predict what she's doing on the court," said 25-year-old Zvonareva.
"You never know what to expect, so you lose your rhythm. Then you start thinking maybe too much on the court. I just know that in that match I will have to concentrate on myself... no matter what's she's trying to do."
(Editing by Alison Wildey)