SPA-FRANCORCHAMPS, Belgium - Lewis Hamilton was pleased to emerge from a tricky qualifying session on the front row of the grid for Sunday's Belgian Grand Prix, but warned he cannot afford to be too aggressive.

The 25-year-old McLaren driver will start alongside pole-sitter Mark Webber of Red Bull after a last gasp effort in the rain saw him nudge Renault driver Robert Kubica back to third position.

The Spa-Francorchamps circuit was dry for the majority of the final qualifying session, but a light shower in the final minutes made it difficult for drivers to make improvements.

Hamilton, the 2008 world champion, believes that he could have taken pole from Webber had he had a good first run, but was happy to have made it on to the front row.

"It was quite a tricky session through the whole qualifying," Hamilton said.

"I got out for my first lap, the first one out. Turn 14 was drying up but I was first one to get there and didn't know how much to push. It was a bit of a disappointing first lap, I wasn't able to hold the time out of the tyres.

"Then I got the opportunity on the second lap which was good lap apart from Turn 1. That was wet and a little bit damp, I lost time there. But the rest of the track was dry and I was able to utilise the tyres and pull out the time.

"I think I was a tenth behind Mark, there was the potential there to be in front in P1, but to be P2 on front row is a good position for us."

Although many suggest that he may be able to make the most of his car's straight line speed and pass Webber on the opening lap, Hamilton warned that he must be cautious because with so many points at stake.

"We are on the front row - the positive thing is we are up there and in for the fight," he said. "I will be aggressive, but I have to be cautious at the same time."

Mclaren team-mate and fellow Briton Jenson Button was not in such good spirits after qualifying in fifth position.

The defending world champion suggested that the unexpected shower in the final minutes of the session prevented him from posting his best time.

"We only had one set of the new option tyres left, so we chose to use them for the last run in Q3," said Button.

"Unfortunately it started to rain - which we hadn't expected - and that cost me 0.3sec in the first sector. It was time I managed to make up in the second and third sectors, but we're fifth."