Webber leads title but Alonso wins in Italy
The Australian had yet another poor start and then a frustrating race, gesticulating angrily as Williams' Nico Hulkenberg went off the track but refused to yield.
"We underperformed as a team," Webber told Belgian TV RTBF.
He might also have been disappointed to finish two positions behind his teammate Sebastian Vettel, despite the young German losing position earlier in the race with a coughing engine.
But with former championship leader Lewis Hamilton crashing out of the race after hitting Felipe Massa, it nonetheless means Webber takes a five-point title lead, albeit now with a much-reduced advantage over the championship chasers.
"The championship is not over," Hamilton told the BBC, "but it's mistakes like I made today that lose world championships."
Fernando Alonso is the big points winner with his popular race win in front of thousands of Ferrari's ardent Tifosi.
The Spaniard was 41 points behind when he drove away from pole position, but that deficit is now halved to 21.
And early Monza leader Jenson Button was 35 points behind before Sunday's race, but by finishing second the gap to the leader is now just 22.
But it might have been a race win for the reigning world champion, who openly questioned McLaren's decision to bring him in for his pitstop behind Alonso's Ferrari team that was ready to pounce.
"It was a little bit disappointing to find myself in that position," said Button, "but I don't think we had the pace of Ferrari today."