Ryan Briscoe went quickest in an eventful third IndyCar practice session in Baltimore.
The Penske driver, who won at Sonoma last weekend, went to the top with a best time of 1:19.7635, edging out Ryan Hunter-Reay by just 0.0011 second.
Rapidly improving track conditions after morning rain meant that several drivers could have had a shot at bettering the Australian's time with their final lap. But JR Hildebrand put paid to that when he caught too much of the curb at the newly-installed chicane and crashed heavily, bringing out a red flag just seconds after the checkered flag had been waved.
Hildebrand's was the fourth stoppage of the morning, with Takuma Sato and Hunter-Reay both causing reds through spins, and EJ Viso triggering one with a crash.
The session gave the drivers the first look at the permanent chicane that was built overnight to prevent cars from launching over the rail tracks on the Pratt Street straight, although the damp surface meant that most took a cautious approach during the first half hour.
Tony Kanaan had lowered the benchmark to 1:31.9703 when James Hinchcliffe bolted on a set of slicks and went 3.7sec quicker, triggering a rush to pitlane and an ongoing succession of plunging lap times.
Current championship leader Will Power finished the morning with the 15th-fastest lap.