The action began on time at the Spanish circuit with Fernando Alonso, Michael Schumacher and Pastor Maldonado braving the conditions.However, both Alonso and Schumacher only completed five laps each with neither setting a time as they went in and out of the pits.
Lewis Hamilton joined the action for McLaren and was the pace-setter at the lunch break with a 1:50.280.
It should be noted, though, that the 2008 World Champion was also the only driver to set a time in the morning session, which saw a total of just 28 laps completed.
Nico Rosberg, meanwhile, replaced Schumacher just before lunch and continued through into the afternoon.
And with the rain continuing throughout the day, the German proved to the quickest in the wet, taking advantage of a slight let-up late in the day.
Rosberg, who covered 35 laps, clocked a 1:43.814 to edge Maldonado by 0.519s.
And although Hamilton improved to a 1:44.560, he had to settle for third place.
Ferrari opted to pack up early with Alonso not running at all in the afternoon.
Times
01. Nico Rosberg Mercedes 1:43.814 35 laps
02. Pastor Maldonado Williams 1:44.333 + 0.519 23 laps
03. Lewis Hamilton McLaren 1:44.560 + 0.746 33 laps
04. Michael Schumacher Mercedes 5 laps
05. Fernando Alonso Ferrari 5 laps
Source: Planet-F1
