Each team is allowed one engine change per car each season, with a second switch resulting in a penalty of 10 grid places.

'We saw a little bit of usage in the engine,' Mercedes Motorsport president Norbert Haug said on Saturday.

'If there was not a 'joker' engine change, we would not have done anything. It's a critical time of the season and if we have it available (we should use it).'

Ferrari's Felipe Massa changed his engine ahead of the previous race in Monza, while championship leader Lewis Hamilton of McLaren still has his backup engine available.

With qualifying to begin at 10pm local time ahead of Sunday's race - the first ever F1 grand prix held at night - both McLaren drivers said the session will be critical given the lack of overtaking opportunities on the street circuit.

'Being a street circuit and maximum downforce, its going to be tough,' Hamilton said.

Kovalainen said overtaking was 'possible' but not likely.

'I would say there is less of a chance of overtaking here than there was in Valencia, which is not a very good sign,' Kovalainen said.

Drivers from all teams had complained about the bumpiness of the circuit after Friday's practice, while otherwise praising the effort local organisers had made to create a challenging circuit for its inaugural race.

'At the beginning of (Friday's practice) session, it was pretty hard core - there are some serious bumps out there,' Hamilton said.

Organisers were forced to make a second late change to the circuit ahead of Saturday's practice and qualifying by altering the entry to pit lane. The white guide line for entry was moved so following cars can see it earlier if a driver is pulling into the pits.

The exit to pit lane is also regarded as a problem, as it puts the drivers immediately into the racing line, and there was no immediate remedy available for this weekend.

'It's always tricky side by side into turn one,' Kovalainen said. 'The pit entry was a bit tricky but now they made some changes.'

On Friday, organisers had to grind down the high curb in the tight turn 10 chicane.

'If you touch the curbs, it doesn't frighten you but you make sure you don't touch it again,' Hamilton said. 'So they're obviously doing their job, aren't they?' -- AP