In a season of surprises, Force India flew up the timesheets in yesterday's free practice for the European Grand Prix.
Germany's Nico Hulkenberg was second fastest in the afternoon, just 0.131 off the pace set by Red Bull's double world champion Sebastian Vettel, while Scotland's Paul Di Resta was sixth.
"Sometimes a car suits one track better than it suits another. You might see something different again this weekend," McLaren's championship leader Lewis Hamilton told reporters.
"Force India looks massively quick this week, so who knows what is going to happen. I don't know where they found their time."
His team mate Jenson Button agreed that their rivals, whose car has the same Mercedes engine as the McLaren, appeared to have found a sweet spot.
"Force India is extremely quick. We haven't seen that really all year, so it seems like somebody else is having their opportunity this weekend," said the 2009 champion.
"They are the team that has been almost competitive but not quite there, but here they seem to be very competitive."
"Our single lap speed looks strong, as does the long run pace, and we appear to have a good feel for the tyres already," said Di Resta.
"Given the pace we have shown today we seem competitive, so hopefully we can challenge for the top 10 in qualifying tomorrow."
McLaren looked well off the pace and Hamilton, 14th on the timesheet, admitted: "I'm about 95 per cent away from where I want to be with my car at the moment, but I'll get back 90 percent overnight. Today has just not been one of those days. I think I know what the problem is, I have just now made all the changes, so I am quite confident that tomorrow will be better."
Hamilton leads Ferrari's Fernando Alonso, racing in front of his home crowd on Sunday, by two points in the championship. Button, whose season has gone into freefall since he won the opening race in Australia, was 12th fastest and sounding less positive.
"We've got a lot of work to do here still," he said.
"We're going to go back on a few things that we changed through the session to a car set-up we know felt reasonably good, but it's difficult to be consistent with that balance because of the front locking. There are a couple of other things that we are thinking about doing for tomorrow morning which could be quite interesting.
"I feel that the changes make a difference and I'm confident we can find a set up that is going to work for us.
"However, whether we will be quick enough to challenge right at the front, I don't know."