Jenson Button continued his domination of top spot on the free practice timesheets at the Japanese Grand Prix by posting the fastest time of Saturday morning's hour-long session, but questions still remain over the true pace of the two Red Bull entries.
After allowing F1's minnows to enjoy their moment in the Suzuka sunshine, Button was the first of the 'big guns' to emerge from the pit-lane and, unsurprisingly, the McLaren vaulted straight to the head of the times, Button lapping quicker within a couple of tours than he did in the equivalent session on Friday morning.
Although both team-mate Lewis Hamilton and world champion elect Sebastian Vettel were quickly on track in pursuit of the Briton, Button remained tantalisingly out of reach, eventually ending the session with a 1min 31.255secs best. The time was nearly seven-tenths quicker than his benchmark from Friday, underlining the development of both the track surface and set-up, and Button had fully half a second in hand over Hamilton as the McLaren duo occupied the top two spots as the chequered flag fell.
Indeed, Button even the luxury of watching the final moments of the session from the sanctuary of the McLaren garage, having completed his morning programme ahead of schedule. He had 13 laps under his belt by that time, while Hamilton continued to circulate, eventually racking up three more laps on his personal tally.
Vettel completed a total of 18 tours, but remained third fastest, moving up the order with a 1min 32.122secs in the closing moments. The RB7 had looked a handful early on, but observers continued to tip Red Bull as the favourites for both qualifying and Sunday's race, despite Button and McLaren having enjoyed the upper hand in terms of practice times throughout the initial running.
The second Red Bull entry, meanwhile, was left to play catch-up after an electrical problem marooned Mark Webber in the pits for much of the opening half hour. The Australian eventually racked up 14 laps, and ended the session in fifth spot, but was 1.146secs off the pace when the flag fell, slotting in behind Ferrari's Fernando Alonso, who was also more than a second behind Button's benchmark.
Webber's cause - at least in terms of not losing to much track time to his rivals - was aided by a red flag midway through the session, caused by Bruno Senna rearranging the front left corner of his Renault after putting two wheels over the outside kerb and spinning hard into the inside wall at the exit of Spoon. The Brazilian was unhurt in the incident, but left his mechanics with a minor mountain to climb in order to have the R31 ready for qualifying. The accident naturally limited Senna to just a handful of laps, and left him down in 17th on the timesheets, but team-mate Vitaly Petrov upheld the team's top ten presence with ninth spot.
That put the Russian behind Felipe Massa, and the Mercedes of Michael Schumacher and Nico Rosberg, while Adrian Sutil claimed the final top ten spot for Force India, deny Sebastien Buemi and Toro Rosso team-mate Jaime Alguersuari. Sutil's gain may have separated him from both team-mate Paul di Resta and the two Saubers on the listings, but only half a second remained between them in terms of lap time, with the two STRs also in the mix for a decent grid slot on Saturday afternoon.
Senna's incident allowed Williams' Pastor Maldonado to move off the bottom of the 'division two' group, but team-mate Rubens Barrichello remained firmly rooted in 18th spot, albeit seven-tenths ahead of Jarno Trulli's Lotus. Williams, however, remain the prime candidate to lose one of its drivers in the opening phase of qualifying.
Lotus continued to have the upper hand among the backmarkers, with Trulli and Heikki Kovalainen finishing ahead of Virgin duo Jerome d'Ambrosio and Timo Glock. Daniel Ricciardo, meanwhile, was handed 23rd spot when HRT team-mate Tonio Liuzzi suffered a repeat of his early Friday exit, the Italian once again being stranded on the run to 130R after his car suffered a water pressure problem after just 8 laps.