Jenson Button put McLaren at the head of the field on the second morning of Formula 1's final preseason test at Barcelona on Friday.
The 2009 world champion's 1m25.936s lap came on medium-compound Pirelli slicks and knocked newly re-signed Force India driver Adrian Sutil off the top spot.
After yet more rain overnight, the session got underway on a damp track and with no serious running taking place inside the first half-hour.
Nico Rosberg was the fastest man in the damp, the German bringing the overall pace down to the 1m30s mark on intermediate tires. The Mercedes driver was also right on the pace when the field collectively switched to slick rubber with an hour to go, following the lead set by Williams driver Pastor Maldonado. The Venezuelan, Adrian Sutil and Fernando Alonso all took turns at the top of the time before Button assumed the top spot with 40 minutes to go.
Sutil wound up 0.215sec slower than the Briton in his Force India, while Sauber's Nico Hulkenberg and Rosberg rounded out the top five.
Romain Grosjean, who was sixth fastest, brought the morning running to a premature halt when his Lotus made what the team termed a "non-specific stop simulation" with three minutes remaining between Turns 8 and 9.
Pos Driver Team Time Gap Laps
1. Jenson Button McLaren 1m25.936s 33
2. Adrian Sutil Force India 1m26.152s + 0.216s 42
3. Nico Hulkenberg Sauber 1m27.246s + 1.310s 36
4. Nico Rosberg Mercedes 1m27.672s + 1.736s 50
5. Romain Grosjean Lotus 1m27.757s + 1.821s 52
6. Fernando Alonso Ferrari 1m27.878s + 1.942s 52
7. Pastor Maldonado Williams 1m29.132s + 3.196s 35
8. Daniel Ricciardo Toro Rosso 1m29.682s + 3.746s 40
9. Max Chilton Marussia 1m29.772s + 3.836s 39
10. Sebastian Vettel Red Bull 1m31.159s + 5.223s 26
11. Giedo van der Garde Caterham 1m39.036s + 13.100s 29
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