* Vettel on pole for third successive race
* Hamilton alongside on front row
* Alonso to start fifth after Webber demotion (Adds detail and quotes)
By Alan Baldwin
YEONGAM, South Korea, Oct 5 (Reuters) - Red Bull's Formula One championship leader Sebastian Vettel grabbed pole position at the Korean Grand Prix on Saturday while closest title rival Fernando Alonso qualified only fifth for Ferrari.
Vettel, who chalked up his third pole position in a row, will have Lewis Hamilton's Mercedes to keep him company on the front row for Sunday's race but the German's car was once again comfortably quicker.
Vettel's flying lap of one minute 37.202 seconds was 0.218 seconds faster than 2008 world champion Hamilton, who had kept him off the top of the timesheets in both Friday practice sessions.
The German is 60 points clear of Alonso in the standings, with five races to go after Yeongam, and is chasing his fourth consecutive win with a fourth successive title fast approaching.
Alonso would have been further down the grid had Australian Mark Webber, Vettel's team mate, not collected a 10 place penalty for taking a post-race 'taxi ride' on the Spaniard's car in Singapore two weeks ago.
Webber, who was on pole in Korea last year, qualified third but will start outside the top 10 with even more of a mountain to climb than Alonso.
"I think it was fairly close. I had a very good lap in Q3 (the final phase), on my first attempt. I knew it would be tricky for me to beat that time, for myself" Vettel said after celebrating his 42nd career pole.
"As expected Mercedes was very strong. So it's a tight battle ... we have got the balance right this weekend and I improved the car from yesterday as I was not entirely happy after practice."
Qualifying conditions were cooler than in practice, although Vettel was also quickest in the final session on Saturday morning, and Sunday could see some rain although the threat of a typhoon has receded.
"I don't mind, it's not a disaster if it starts to rain, we have rain tyres in the garage," said the 26-year-old.
"When I arrived on Wednesday, it was very windy but it has died down since then and I think the typhoon has changed direction."
Vettel and Alonso are the only drivers to have won in Korea since the race made its debut in 2010 and Red Bull's triple champion is chasing his hat-trick at Yeongam.
Alonso has made storming starts his trademark this season and was confident he would have plenty of overtaking opportunities even if he might have to bide his time.
"Here, for the first corner there is not enough space to really attack and so we pass one by one through turn one. So we will try to attack in turn three and turn four," he told reporters.
"(It) will be not too difficult to overtake with the two DRS (drag reduction system) points. So the start will not be as crucial as maybe Singapore," added Alonso.
The Spaniard will have both Mercedes drivers ahead of him with Nico Rosberg lining up in fourth place and Lotus's Romain Grosjean in third, right behind Vettel.
"We got the most out of the car. It has been a good qualifying for us and hopefully tomorrow we will be able to fight with them (Red Bull)" said Hamilton. "There's threats all around but I'm looking forward.
"A couple of years ago, I was on pole and Seb got past me at the start, so I'd like to repay him on that one."
Both the Saubers made it into the top 10, with Nico Hulkenberg to start seventh.
For only the second time this season, neither of the McLarens made it through to the final session with Mexican Sergio Perez qualifying 11th and 2009 champion Jenson Button alongside in 12th.
Both Williams drivers, Venezuelan Pastor Maldonado and Finland's Valtteri Bottas, failed to make it through the first phase.
Marussia's French driver Jules Bianchi was reprimanded and given a three place demotion - meaningless since he qualified on the back row anyway - for impeding Force India's Paul Di Resta, who qualified 15th. (Editing by Peter Rutherford/Amlan Chakraborty)