The Ducati Marlboro star felt he was being careful, so it was a 'big surprise' when he was caught out by the conditions.
"I made a mistake and crashed, even though I was being very careful at that point of the track because I had seen a lot of 125 riders crashing and running wide there, so it came as a big surprise to me," said the Australian. "For the rest of the session we only had medium tyres so it wasn't possible to ride with so much confidence."
Nevertheless Stoner, who holds a huge 60 point lead over
Valentino Rossi coming into the San Marino GP, still set the third fastest time - before a torrential downpour flooded the circuit and forced the cancellation of the two afternoon sessions.
"I was expecting this afternoon to be dry but it was the complete opposite - in the end there was enough water on the track in some places to go swimming! I think we could have had a good day today, I was quite disappointed that we couldn't ride the circuit again," he said.
The laps he did complete left Stoner - in contrast to second fastest Rossi - unimpressed by the quality of the circuit.
"I'm not so impressed with the track, there are some points where it's very, very bumpy and also the circuit in some places is unbelievably slippery in the wet, it's similar to
Donington and worse at some corners," stated Stoner, aiming to hand Ducati its first ever home
MotoGP win on Sunday. "It's not so easy to get a good feeling in the wet here but hopefully it will be dry tomorrow and then we should be able to understand it a little bit better."
Team-mate
Loris Capirossi was just one place behind Casey on the timesheets, but disagreed with the Australian over the amount of grip available.
