Kral, who raced in the season-opener for Barwa Addax Team at Sepang in Malaysia, was dropped in favour of Dani Clos for the recent Bahrain double-header. With Clos making his Formula 1 race weekend debut with HRT in free practice, a fired up Kral returned and banged in his 1m31.109s, 10 minutes into the session.
Before Kral hit the front, most-recent round winner Tom Dillmann set the early pace for Rapax before he was knocked off the top spot by first Felipe Nasr of DAMS and then Caterham Racing's Giedo van der Garde.
Britain's James Calado kept his powder dry in the pitlane in the early stages before going out to set the second-fastest time for Lotus GP, his 1m31.168s just 0.059s off the pace. Nasr stayed third, ahead of van der Garde and Dillmann.
Points dominator Davide Valsecchi was sixth-fastest for DAMS, the Italian suffering a flapping left-sidepod turning vane. Second in points, Luiz Razia, was only 10th fastest for Arden International.
Calado's Lotus team-mate Esteban Gutierrez was down in 18th after a series of brake lock-ups from the man who lies third in the championship.
Laps were limited in practice, as Pirelli has mandated the soft-compound option tyre for this event, which is likely to be used effectively as a qualifying tyre this afternoon.
As teams are limited with their scope for laps on the prime tyre, the drivers didn't complete a huge amount of running - only five got into double figures during the 30-minute session.
1. Josef Kral Barwa Addax Team 1m31.109s 7
2. James Calado Lotus GP 1m31.168s 7
3. Felipe Nasr DAMS 1m31.238s 7
4. Giedo van der Garde Caterham Racing 1m31.246s 6
5. Tom Dillmann Rapax 1m31.358s 7
6. Davide Valsecchi DAMS 1m31.396s 11
7. Fabrizio Crestani Venezuela GP Lazarus 1m31.400s 12
8. Jolyon Palmer iSport International 1m31.476s 6
9. Stefano Coletti Scuderia Coloni 1m31.832s 7
10. Luiz Razia Arden International 1m31.717s 6
11. Fabio Leimer Racing Engineering 1m31.799s 6
12. Fabio Onidi Scuderia Coloni 1m31.832s 7
13. Johnny Cecotto Barwa Addax Team 1m31.870s 5
14. Max Chilton Carlin 1m31.895s 9
15. Rodolfo Gonzalez Caterham Racing 1m31.913s 9