"A fastest lap could be possible but I'm not sure about a podium, " the German said.
Alonso's fastest lap was more than 0.7secs quicker than Webber's, in a similar series of runs, on Thursday.
The Spaniard also completed a race simulation run in the afternoon session, with a fastest lap of 1:21.669.
Julian Simon of Aprilia claimed pole position in the 125cc category with a fastest lap of one minute 48.237 seconds.
The 39-year-old, who was third in qualifying, recorded the second-fastest lap in the minor series event at the Misano circuit in Italy.
Vettel's second fastest lap was in sharp contrast to Red Bull team-mate Mark Webber's performance, with the Australian's car suffering suspected engine failure.
The qualifying session saw Spain's Lorenzo briefly threatened to spoil Stoner's party when he recorded the fastest lap with fewer than 15 minutes remaining.
Patrick, who is still looking for her first win in Nascar, earned the top spot after recording the fastest lap time during qualifying last weekend.
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The wet weather slowed down the drivers considerably, Webber's time three seconds slower than the fastest lap of the week, set by Ferrari's Felipe Massa.
Mark Webber's Red Bull was just 0.024 seconds behind Hamilton's fastest lap of one minute 20.472secs, which is the fastest of the four days at Barcelona.
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Nick Heidfeld, who set the fastest lap in final practice, kept up his improved run of form to take fifth for BMW Sauber with team-mate Robert Kubica in eighth.
Even though several days of cold, wind and rain gave way to warmer spring temperatures at Phillip Island, the Spaniard was feeling under the weather, struggling to the sixth fastest lap time.
Regardless of the fact that Alonso is light on fuel, the team have made progress - we saw at the German Grand Prix that Renault had the fastest lap of the race.
But Button responded with a new fastest lap of the race to take his third win of the season and a first in Japan, which he has described as his second home.
"It was looking really good and I had just done the fastest lap of the race again - I think I did it on the second lap and then again on lap 10, " he said.
The Spaniard traded fastest lap times with team-mate Sebastien Buemi in a quiet opening half hour and improved his lap time by over six seconds, but he still finished the session in 20th position, one place behind his team-mate.
Unlike Hulkenberg, who set his fastest lap on one short run, Alonso's was set during a number of formidable-looking runs, in which he produced a set of consistently quick times around the same pace as his fastest lap time.
Felipe Massa in the other Ferrari set the race's fastest lap and he, too, might have leapfrogged Barrichello - had he not been stuck behind the newly refuelled and therefore slower Button when he needed to be banging in the fast low-fuel laps.
Crafar's pole position, fastest lap and race win sweep was astounding not only because it was achieved on Dunlop tyres, who had not won for three years in an era dominated by Michelin, but also because it was Yamaha's first in 23 races.
It is amazing to think that just four years ago, MotoGP riders Jorge Lorenzo and Andrea Dovizioso were crossing the line side by side in the 125cc race at this very circuit (the only dead heat on record in any class of MotoGP, although Lorenzo was given the win because he had the fastest lap, trivia fans).
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The Yamaha ace won both Superbike and Supersport races while Ian Hutchinson from Yorkshire set a new fastest ever road race lap with 130.828mph.
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Last year, Harper's fastest home-run lap lasted 16.2 seconds.
After three of the four days of running, Schumacher has set the fastest time in Jerez with a lap he recorded on the second day.
There was no letting up by Anstey on the final lap, and again he was fastest round the course to the delight of the travelling contingent from New Zealand.
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Fernando Alonso was only ninth fastest and Monaco winner Jarno Trulli failed to complete his lap because of problems with the electronics in his steering wheel, which affected the gearbox.
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Red Bull's Sebastian Vettel, whose team-mate Mark Webber set the fastest time of the first day of the test, was fifth fastest, just dipping under the Australian's best lap with a 1:21.258.
For the second day running, Sebastien Buemi was fastest in Toro Rosso's 2008 car with a best lap of 1:17.591 at Jerez.
Mercedes' Nico Rosberg, who set the fastest time in first and second qualifying sessions, retired on lap 27 due to an electrical failure, while Sauber driver Nico Hulkenberg did not even start the race due to a fuel-system problem.
Hamilton produces a stunning lap of 1:27.373 to set the fastest time.
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