Fernando Alonso grabbed the fastest time in a Ferrari one-two as wet weather frustrated the Formula 1 field's attempts to get an early understanding of the Spanish Grand Prix upgrade packages in opening practice at Barcelona.
It was only coming into the final quarter of an hour that slicks were viable, and even then there were sufficient slippery patches to limit the relevance of the laps that drivers managed.
But with so many developments to try, teams were less reticent about coming out early than is often the case in wet sessions.
The Spanish crowd therefore had a decent amount of track activity to enjoy all morning, and would also have appreciated seeing home hero Alonso on top of the times for much of the session.
Alonso spent a while as the fastest man during the wet running, though he tumbled down the order as conditions improved.
Going into the closing seconds, his Ferrari team-mate Felipe Massa was the latest to burst to the top of a constantly fluctuating timing screen as everyone got up to speed on slicks.
But Alonso finished the morning with a flourish, setting a 1m25.252s lap to beat his team-mate by 0.203 seconds.
Toro Rosso's Jean-Eric Vergne had starred by being the first man to get slicks to work, and he remained consistently up front for the rest of the session, ending up third.
Romain Grosjean had an early spin into the hairpin at the end of the back straight, before finishing the session fourth for Lotus.
Adrian Sutil's Force India, Lewis Hamilton's Mercedes and Valtteri Bottas's Williams were next up in an inevitably shuffled order, with Kimi Raikkonen, Nico Rosberg and Paul di Resta completing the top 10.
Jenson Button was the only driver not to attempt a flying lap, though he did six exploratory tours in the updated McLaren.
Red Bull also hung back when the track dried, with Sebastian Vettel and Mark Webber at the foot of the top 20.
Pos Driver Team Time Gap Laps 1. Fernando Alonso Ferrari 1m25.252s 20
2. Felipe Massa Ferrari 1m25.455s + 0.203s 20
3. Jean-Eric Vergne Toro Rosso-Ferrari 1m25.667s + 0.415s 25
4. Romain Grosjean Lotus-Renault 1m26.042s + 0.790s 21
5. Adrian Sutil Force India-Mercedes 1m26.212s + 0.960s 24
6. Lewis Hamilton Mercedes 1m26.374s + 1.122s 19
7. Valtteri Bottas Williams-Renault 1m26.456s + 1.204s 20
8. Kimi Raikkonen Lotus-Renault 1m26.614s + 1.362s 21
9. Nico Rosberg Mercedes 1m26.621s + 1.369s 21
10. Paul di Resta Force India-Mercedes 1m26.755s + 1.503s 16
11. Daniel Ricciardo Toro Rosso-Ferrari 1m26.940s + 1.688s 26
12. Nico Hulkenberg Sauber-Ferrari 1m27.061s + 1.809s 24
13. Sergio Perez McLaren-Mercedes 1m27.135s + 1.883s 6
14. Esteban Gutierrez Sauber-Ferrari 1m27.250s + 1.998s 26
15. Pastor Maldonado Williams-Renault 1m27.576s + 2.324s 24
16. Heikki Kovalainen Caterham-Renault 1m28.373s + 3.121s 14
17. Giedo van der Garde Caterham-Renault 1m28.600s + 3.348s 19
18. Jules Bianchi Marussia-Cosworth 1m28.887s + 3.635s 14
19. Sebastian Vettel Red Bull-Renault 1m29.457s + 4.205s 11
20. Mark Webber Red Bull-Renault 1m29.473s + 4.221s 21
21. Rodolfo Gonzalez Marussia-Cosworth 1m30.314s + 5.062s 13
22. Jenson Button McLaren-Mercedes no time 6