The racer clocked 1:46.286 ahead of newcomer Kevin Giovesi and Super Nova teammate Vittorio Ghirelli.
Karthikeyan drove for Zele Racing in the first three rounds of 2013 before securing a last-minute deal at Super Nova.
The 36-year-old driver earned 34 points in six races while driving for Zele.
The opening race at Silverstone takes place later in the day and Karthikeyan is looking forward to it after being fastest in today's qualifying and two practice sessions yesterday.