British driver Jenson Button ended a three-year wait for pole position by finishing fastest in Belgian Grand Prix qualifying, while defending champion Sebastian Vettel will start Sunday's race from 10th place.
Button, who won the season's opening GP in Australia, overcame earlier balance problems to grab his first pole of the season on Saturday, the eighth of his career and his first ever in his 50th race for McLaren.
"It's been quite a long time since I got my last pole position, back in 2009 in Monaco. It's been emotional," said Button, who won the F1 title that year with the Brawn team. "Maybe a five-week break between every race is what I need ... I'm getting old now."
The 32-year-old Button seemed to be struggling earlier in the day with the understeering of his car, but got it right when it mattered with a best lap of 1 minute, 47.573 seconds.
"A great qualifying session, the engineers have really been on it today," Button said. "I just got the balance right. We just tickled it, especially through qualifying. The balance is to my liking. It's difficult to find a car that works for me in qualifying but when it does we get pole position."
Button, vying for his 14th GP win, is seventh in the championship and 88 points behind overall leader Fernando Alonso of Spain.
"I think I'll have to finish ahead of Fernando in every race from now on to finish ahead of him," Button said.
It has been one of the most unpredictable seasons for years, and that trend looks set to continue in Spa with unheralded driver Kamui Kobayashi of Japan starting second place.
"In yesterday's practice we really struggled a lot, but this morning we improved a lot," said Kobayashi, who got his best ever qualifying position. "We didn't really know how much the track conditions would improve. Tomorrow is a different story, and we need to fight."
Kobayashi is only the second Japanese driver to start on the front row after Takuma Sato in 2004 at the Nurburgring.
Pastor Maldonado of Venezuela posted the third fastest time in qualifying, but he was demoted three grid positions to sixth for holding up Force India's Nico Hulkenberg on a turn, meaning that Kimi Raikkonen moves up one place to third, Sergio Perez goes to fourth and Alonso to fifth.
Maldonado, who won the Spanish GP in May, nevertheless showed the potential of the Williams car, and was quickest in the first qualifying session.
"I adapted to the different conditions," Maldonado said before learning of his penalty.
Vettel's bid to catch Alonso looks to have taken another blow, while his Red Bull teammate Mark Webber will start the race with a five-place grid penalty, knocking him down from seventh to 12th, with McLaren's Lewis Hamilton moving up from eighth to seventh.
"There was no problem, I just wasn't quick enough," said Vettel, who is 42 points adrift of Alonso overall. "The speed wasn't there."
Hamilton, who is fourth overall, has vowed to work for Button on Sunday.
"It has not been a great qualifying session for me," Hamilton said. "I will try and do as best I can to back Jenson up tomorrow."
Alonso posted the fastest time in Saturday's third practice, where drivers frantically fine-tuned their cars for qualifying.
Heavy rain marred Friday's two practice runs, restricting drivers to a handful of laps, so the emphasis was on cramming as much testing as possible with the Spa circuit splashed in bright sunshine and completely dry.
Some drivers found themselves at odds with their cars as they tried to compensate for lost time on Friday.
Button had complained to his McLaren team that "we've got to look at the balance," while Mercedes driver Nico Rosberg pulled out after five laps, and his day got worse as he incurred a five-place grid penalty for a gearbox change.