Castroneves, driving the No. 3 Team Penske car, had a quick lap of 52.3901 seconds on the 1.67-mile, 11-turn circuit as drivers prepare for the season-opening Honda Grand Prix of St. Petersburg on the temporary 1.8-mile street course.

Hunter-Reay had a best lap of 52.5733 seconds in the No. 28 DHL/Sun Drop Citrus Soda car for Andretti Autosport.

Click it: Combined session results

The session continues until 5 p.m. A second group of drivers will test at Sebring on March 8-9. The Open Test is open to the public each day (9 a.m.-5 p.m.). There is a $10 admission charge. Firestone Indy Lights will conduct an Open Test at the facility Feb. 7.

Open Test lineup by groups

Group 2 (9 a.m.-noon and 1-5 p.m. March 8-9):

No. 4 JR Hildebrand (Panther Racing) – Chevrolet
No. 5 E.J. Viso (KV Racing Technology) – Chevrolet
No. 6 Katherine Legge (Lotus Dragon Racing) – Lotus
No. 7 Sebastien Bourdais (Lotus Dragon Racing) – Lotus
No. 8 Rubens Barrichello (KV Racing Technology) – Chevrolet
No. 9 Scott Dixon (Target Chip Ganassi Racing) – Honda
No. 10 Dario Franchitti (Target Chip Ganassi Racing) – Honda
No. 11 Tony Kanaan (KV Racing Technology) – Chevrolet
No. 14 Mike Conway (A.J. Foyt Racing) – Honda
No. 15 Takuma Sato (Rahal Letterman Lanigan) – Honda
No. 20 Ed Carpenter (Ed Carpenter Racing) – Chevrolet
No. 22 Oriol Servia (Lotus Dreyer & Reinbold Racing) – Lotus
No. 38 Graham Rahal (Service Central Chip Ganassi Racing) – Honda
No. 67 Josef Newgarden (Sarah Fisher Hartman Racing) – Honda
No. 77 Alex Tagliani (Team Barracuda – BHA) – Lotus
No. 83 Charlie Kimball (Novo Nordisk Chip Ganassi Racing) – Honda IndyCar