"Theo took a while to get into the game - but once he scored the goal, you saw him much more," said manager Arsene Wenger. "When the space opened up behind them you could see his pace and also that he is clinical in front of goal.
"He did not panic with the first one - and with the second goal, there was a really clinical finish."
Wenger is confident Walcott is one of England's outstanding prospects.
"If you look across the country, you complain that you do not have many strikers -Theo is one of them.
"I believe he has the talent - that is why he is at Arsenal. The problem is not to hurry too much.
"He has good ingredients in him. He is intelligent, has fantastic pace - and his technique is improving. But you need to be patient."
"He is a very talented player. We were not able to handle his pace," admitted Slavia coach Karel Jarolim.