Button keeps McLaren ahead in practice

McLaren resumed its morning superiority early in the session, with Lewis Hamilton and Button first and second following the initial runs.

Indeed at the halfway point afternoon practice looked extremely symmetrical, with the two McLarens heading the Red Bulls, Mercedes, Renaults, Saubers and Force Indias in two by two formation through the top 12.

The neat order was shuffled soon afterwards. Hamilton switched to softer tyres with 40 minutes to go and trimmed 0.020 seconds from his time to get down to 1m28.672s - but moments later Vettel went quicker still on the same tyres, lapping in 1m28.590s.

He stayed in front for five minutes before Button put McLaren back in front with a 1m28.280s lap, which remained the best of the session.

Webber then took second from Vettel, but the afternoon came to a worrying end for Red Bull as the Australian came to a halt on track five minutes from the end, with wisps of smoke from the car's rear. While he neatly reversed the car back behind the barriers, Vettel was already expressing concern over his water pressure via the radio, giving the championship-leading team cause for some reliability anxiety.

Hamilton remained fourth until the end, with Fernando Alonso bringing Ferrari up to fifth by the chequered flag after a low-key start to the afternoon.

Mercedes was sixth and seventh, Nico Rosberg ahead of Michael Schumacher this time, followed by the Renaults and Felipe Massa in the second Ferrari.

Turn 8 continued to cause headaches for drivers. Tonio Liuzzi caught a high-speed half-spin at the long, fast corner without emulating his Force India team-mate Adrian Sutil's morning impact with the barriers.

Three-time Istanbul winner Massa had a few early scares at Turn 8 too, before later snapping into a wild slide that - like Liuzzi - he caught just before it turned into a full spin, though his long sideways drift still ruined his soft tyres.

Pos  Driver         Team                     Time              Laps
 1.  Button         McLaren-Mercedes         1:28.280            30
 2.  Webber         Red Bull-Renault         1:28.378  + 0.098   24
 3.  Vettel         Red Bull-Renault         1:28.590  + 0.310   26
 4.  Hamilton       McLaren-Mercedes         1:28.672  + 0.392   32
 5.  Alonso         Ferrari                  1:28.725  + 0.445   30
 6.  Rosberg        Mercedes                 1:28.914  + 0.634   22
 7.  Schumacher     Mercedes                 1:28.974  + 0.694   22
 8.  Kubica         Renault                  1:29.225  + 0.945   34
 9.  Petrov         Renault                  1:29.501  + 1.221   36
10.  Massa          Ferrari                  1:29.620  + 1.340   26
11.  Sutil          Force India-Mercedes     1:29.629  + 1.349   16
12.  Hulkenberg     Williams-Cosworth        1:29.987  + 1.707   17
13.  Kobayashi      Sauber-Ferrari           1:30.053  + 1.773   34
14.  de la Rosa     Sauber-Ferrari           1:30.176  + 1.896   34
15.  Buemi          Toro Rosso-Ferrari       1:30.386  + 2.106   32
16.  Liuzzi         Force India-Mercedes     1:30.627  + 2.347   28
17.  Barrichello    Williams-Cosworth        1:30.766  + 2.486   32
18.  Alguersuari    Toro Rosso-Ferrari       1:30.933  + 2.653   37
19.  Kovalainen     Lotus-Cosworth           1:31.610  + 3.330   37
20.  di Grassi      Virgin-Cosworth          1:33.013  + 4.733   28
21.  Trulli         Lotus-Cosworth           1:33.081  + 4.801   11
22.  Glock          Virgin-Cosworth          1:33.312  + 5.032   29
23.  Senna          HRT-Cosworth             1:33.420  + 5.140   35
24.  Chandhok       HRT-Cosworth             1:33.740  + 5.460   25

All Timing Unofficial