Highlights - Fernando Alonso wins Italian Grand Prix
By Andrew Benson
BBC Sport at Monza
Ferrari's Fernando Alonso leapt back into title contention after winning a thrilling battle with McLaren's Jenson Button in the Italian Grand Prix.
The Spaniard moves up to third in the championship, 21 points behind new leader Mark Webber of Red Bull, who leapfrogged McLaren's Lewis Hamilton.
Webber finished sixth at Monza, while Hamilton retired after a collision with Ferrari's Felipe Massa, who came third.
Button stays fourth overall, ahead of Red Bull's Sebastian Vettel.
The German finished fourth in a race that Red Bull had always viewed as damage limitation, one place ahead of the Mercedes of Nico Rosberg.
The result in Italy means less than a win covers all five title contenders.
The decisive moments of the race came around laps 36 and 37.
Button had led from the start after passing Alonso into the first chicane following a slow getaway from the Spaniard, who started from pole position.
Button frustrated by lack of McLaren pace
Alonso tracked Button all through the first part of the race, with the Englishman's lead ebbing and flowing as the two traded fastest laps in a fascinating flat-out battle.
By lap 13, Button had eked out a lead of 1.6 seconds, but Alonso then came back at him and they were nose to tail by lap 20.
A series of fastest laps from Button stretched his lead to a second on lap 29, but again Alonso responded.
Button pitted first, on lap 36, with Alonso coming in next time around. A brilliant in-lap followed by a pit stop that was 0.8secs quicker than McLaren's meant Alonso exited the pits just ahead of Button.
He had to defend forcefully at the first chicane, but held Button off around that lap and then proceeded to pull away at a pace to which Button could not respond.
"Most of the thanks for the win is to the mechanics," said Alonso.
"The pit stop felt so quick. I stopped, they changed tyres and there was a green light. I didn't even have first gear in.
"When I came out of the pits I saw he was quite far behind and I thought OK, we have done it but I forgot he was coming at 320kmh (199mph) and he closed very fast.
"We went in the first corner nearly side by side and then I nearly spun when I got on the throttle."
Button was left to worry about Massa, who was slightly faster than him in the closing laps but was unable to get close enough to challenge.
"It was quite a tough race mentally to have Fernando behind me for most of it, very mentally draining, and then we pitted one lap early," said the Briton.
"The team think the prime tyre was faster but for me I couldn't find the grip on the first lap. So we made a bit of a mistake there.
"It's a happy day but obviously you want to be first.
"I didn't have the pace I expected in the race - these guys [Alonso and Massa] were super-fast.
"I was surprised how close they could stay in the fast corners.
"We had a very quick car but I think these guys had a slight edge."
Hamilton's hopes ended at the second chicane on the first lap as he was trying to take advantage of a battle between the two Ferrari drivers.
Alonso was delayed by his battle with Button at the first corner and Massa was able to get alongside him through the second, left-handed part of the chicane.
That gave Massa the inside line through the following Curva Grande, but Alonso was on the inside approaching the second chicane and held on to second position.
Hamilton, though, was right behind him, hoping to pass Massa on the inside, but as they turned into the corner he was not close enough.
Massa's rear wheel hit Hamilton's front and broke the suspension of the McLaren.
Hamilton crashes out at Monza on lap one
"I had a good start and gained a position," Hamilton said.
"In a realistic world I perhaps should've stayed there a while. I put my car up the inside and tried to get third - it was obviously a little bit too much. I'm very disappointed in myself and sorry for the team.
"I've got to try to collect my thoughts and move onto the next race. The championship is not over, but it's mistakes like I made today that lose world championships."
Vettel recovered from a brief engine glitch, which lost him a place to team-mate Webber, by making an ultra-late pit stop for a new set of tyres at the start of the last lap.
The extra time he spent out on the track leapfrogged him ahead of Webber, Williams's Nico Hulkenberg and Renault's Robert Kubica, all of whom he had been behind before they made their stops.
The pit lane was closed for a brief period during the race while medics tended to an injured Hispania Racing team member, who was subsequently transferred to the circuit medical centre.
Sakon Yamamoto accelerated away after his pit stop, striking the head of the team member with his rear wing.
"I was very worried about the incident in the pit lane," said Yamamoto, who finished the race. "I asked if he was OK and I was told that he was not badly injured."
Hispania Racing was fined $20,000 (approximately £13,000) for an unsafe release of Yamamoto's car. Team boss Colin Kolles said: "He remained conscious. We now wish that he recovers quickly."