INDIANAPOLIS - Sam Hornish Jr. just keeps pumping out fast laps at the Indianapolis Motor Speedway.

Every scheduled session since the track opened last week for practice for the May 28 Indianapolis 500 has been shortened or canceled by rain. No matter to two-time IRL IndyCar Series champion Hornish, whose Honda-powered Dallara has shot to the top of the speed chart in every session but one.

Thursday was no exception, with Hornish beating back a strong challenge for the day's fastest lap from Marlboro Team Penske teammate Helio Castroneves with a speed of 224.941 mph.

"We wanted the chance to run in traffic this afternoon, which we were able to do, and I'm happy with the way the car is handling in the pack," Hornish said. "Tomorrow, we'll work some more on race setup and we'll spend the last part of the day preparing for qualifying on Saturday."

Two-time Indy winner Castroneves was close behind Thursday at 224.437, followed by defending champion Dan Wheldon, the only driver to beat Hornish this month. Wheldon, driving for Target Chip Ganassi Racing, posted the fastest lap so far (228.663) during a brief practice session Sunday, with Hornish right behind at 228.220.

Scott Dixon, Wheldon's teammate, was fourth fastest at 222.461, followed by Scott Sharp at 222.425, Jeff Simmons at 221.716, Tony Kanaan at 221.707, rookie Townsend Bell at 221.329, and Tomas Scheckter at 221.299.

Danica Patrick, the only woman entered in the race for the second straight year, was 11th fastest at 220.900.

The rain came early and late Thursday, delaying the start of the six-hour practice session by nearly four hours and then cutting it short by another 18 minutes. In between, 31 cars made it onto the 2.5-mile oval, turning a total of 1,050 laps.

Rain also washed out both scheduled days of qualifying last weekend, meaning the entire 33-car field will have to be filled in time trials Saturday and Sunday. With the track closed Monday and Tuesday and rain again shortening Wednesday's practice, the pressure is on, especially for the drivers who didn't get onto the track at all last week or only ran in rookie orientation May 7 and 8.

Two of the rookies, Arie Luyendyk Jr., son of a two-time Indy winner, and Thiago Medeiros crashed Thursday in separate incidents in the first turn.

"It was our first lap," said the disappointed Luyendyk. "I wasn't even to speed yet. I couldn't have been going faster than 180. I tried to save it and stay out of the wall, but we made contact. It's a shame because we need the laps more than anyone else out there."

Medeiros had just turned a lap of 213.221 before he crashed, hitting the wall considerably harder than Luyendyk. Both drivers were checked at the infield medical center and released to drive, but Medeiros has no backup car.

"I saw Kosuke (Matsuura) behind me and I was waiting for him to overtake me," Medeiros said. "I moved up a little bit and lost it. I'm just disappointed. It's over."