Spanish GP: Sebastian Vettel heads Fernando Alonso in practice
Red Bull's Sebastian Vettel narrowly beat Ferrari's Fernando Alonso to set the pace in Friday practice at the Spanish Grand Prix.
The German was just 0.017 seconds ahead of the man he beat to last year's title, with the second Red Bull of Mark Webber 0.066secs behind the Spaniard.
Lotus driver Kimi Raikkonen was fourth fastest, 0.222secs off the pace, ahead of Ferrari's Felipe Massa.
The Mercedes of Lewis Hamilton and Nico Rosberg took sixth and seventh.
Force India's Adrian Sutil and Paul di Resta were eighth and 10th, split by the Toro Rosso of Jean-Eric Vergne, whose team-mate Daniel Ricciardo was 11th.
"Overall, we can be happy with today," said Vettel. "This morning was a waste of time. This afternoon was fairly conclusive.
"In terms of pace we are there or thereabouts with the top guys."
Pirelli have brought a revised version of the hard tyre to this race, which is slightly harder than the one used so far this season and has a lower operating temperature window. Vettel said he did not think it would make much difference to how long the tyres lasted during the race.
"Difficult to say too much in the new hard tyre," he said. "We didn't expect any miracle and I don't think it's a massive difference. We will see how it behaves on Sunday and I don't think it helps us in terms of changing the race, so we will see a similar amount of pit stops as the last race."
"It's been OK," said Hamilton. "Not the greatest of days but we've learnt a lot and we have a lot of work to do to find out where we can improve with the balance.
"We've added downforce so that's a positive. I'm very happy with the work everyone has done; we just have to extract it."
On the high-fuel, race-simulation runs, the Ferrari and the Lotus appeared the quickest cars, with Raikkonen marginally fastest from Alonso and some way ahead of the Red Bulls, which tend to use a higher fuel load on these laps.
Mercedes again appeared to be struggling for race pace, with the car significantly slower than the Lotus, Ferrari and Red Bull form the start of the runs and its lap times fading away much faster.
BBC 5 live analyst and former F1 driver Allan McNish said: "Ferrari look to have a strong car in all conditions and on both tyres but it's the usual cars at the front.
"Mercedes are going to have to take some pace out of the car in qualifying or they are going to be in trouble with degradation in the race."
In the dry second session, Force India's Paul di Resta suffered a tyre failure very similar to the one experienced by Hamilton in the last race in Bahrain.
Massa also suffered two tyre failures in Bahrain, both of which Pirelli said were caused by debris.
BBC F1 technical analyst Gary Anderson said he suspected the recurring problems were being caused by the cornering forces of the cars shearing the bond between the rubber and the carcass.
Many of the teams were trying out significant upgrades to their cars and none were more important than those of McLaren, who have had a poor start to the season.
The car features more tightly-packaged bodywork and a new front wing but the performance suggested the team had not made a huge step forward.
Jenson Button was 12th, 1.498secs behind Vettel. Team-mate Sergio Perez was 13th, 0.548secs behind the Englishman.
BBC 5 live analyst Allan McNish said: "From the times and the way the car looks on track, it still seems to be a work in progress for McLaren right now."
McLaren sporting director Sam Michael said: "We don't expect to go from sixth to the front row straight away.
"That is why we have managed expectation, so people don't think that is what we are claiming to do.
"We know the bits we have to work on, we know where our issues are and we know what is in the pipeline. It is going to take time."
Williams, who have also had a troubled start to the season, have their own upgrade package but like McLaren did not appear to be any further forward.
Valtteri Bottas was 14th, two seconds off the pace, with team-mate Pastor Maldonado 16th.
1. Sebastian Vettel (Ger) Red Bull 1min 22.808secs
2. Fernando Alonso (Spa) Ferrari 1:22.825
3. Mark Webber (Aus) Red Bull 1:22.891
4. Kimi Raikkonen (Fin) Lotus 1:23.030
5. Felipe Massa (Brz) Ferrari 1:23.110
6. Lewis Hamilton (GB) Mercedes 1:23.140
7. Nico Rosberg (Ger) Mercedes 1:23.398
8. Adrian Sutil (Ger) Force India 1:23.840
9. Jean-Eric Vergne (Fra) Toro Rosso 1:24.058
10. Paul Di Resta (GB) Force India 1:24.104
11. Daniel Ricciardo (Aus) Toro Rosso 1:24.175
12. Jenson Button (GB) McLaren 1:24.306
13. Sergio Perez (Mex) McLaren 1:24.854
14. Valtteri Bottas (Fin) Williams 1:24.888
15. Nico Hulkenberg (Ger) Sauber 1:25.167
16. Pastor Maldonado (Ven) Williams 1:25.321
17. Esteban Gutierrez (Mex) Sauber 1:25.441
18. Romain Grosjean (Fra) Lotus 1:25.851
19. Giedo van der Garde (Ned) Caterham 1:25.963
20. Jules Bianchi (Fra) Marussia 1:26.078
21. Charles Pic (Fra) Caterham 1:26.930
22. Max Chilton (GB) Marussia 1:26.970
Spanish Grand Prix, day two
- Saturday, 11 May:
- Third practice: 09:55 BST live on BBC Two and BBC Radio 5 live sports extra, live text commentary online. Qualifying: 12:10 BST live BBC One, 12:55 BST on 5 live sports extra, live text commentary online.
Spanish Grand Prix, day three
- Sunday, 21 April:
- Race: 12:10 BST live BBC One and 13:00 on 5 live, live text commentary online.