* Hamilton fastest in both practice sessions
* Vettel second quickest
* Raikkonen crashes in morning (Adds Alonso, Brawn, Raikkonen quotes)
By Alan Baldwin
YEONGAM, South Korea, Oct 4 (Reuters) - Lewis Hamilton kept championship leader Sebastian Vettel off the top of the timesheets in both Friday practice sessions for the Korean Formula One Grand Prix while Kimi Raikkonen slammed his Lotus into a tyre wall in the morning.
The Mercedes driver lapped the anti-clockwise Yeongam circuit, set against a backdrop of coastal marshes and South Korean shipyard cranes, with a best time of one minute 39.630 seconds in the morning and 1:38.673 after lunch.
Red Bull's Vettel, chasing his fourth win in a row since the end of August and third in succession in Korea, was second quickest in both sessions run in bright sunshine and under cloudless skies.
"I feel like I have a bit of a better foundation this weekend. I can't remember the last time I had a really strong Friday," said Hamilton.
"We haven't changed anything but the day just went smoothly and all the processes with the team worked well."
Vettel was a mere 0.037 slower in the first, after firing in his best lap in the closing seconds, and 0.108 adrift in the second.
"I think it will be very close this weekend with Mercedes," said the German, who has a 60 point lead over Ferrari's Fernando Alonso with six races to go and could clinch his fourth successive title this month.
Alonso, who was sixth and seventh in the sessions, sounded gloomy afterwards.
"On this track too it's aerodynamics that make the difference and for that reason, I am not expecting too many surprises when compared to the last few Grands Prix," said the Spaniard.
"The time sheet follows the order that continues to be more or less the same seen in previous weekends and there is every probability that, again here, we can expect to struggle in the race."
On a quiet opening day, with largely empty stands at the track some three hours by KTX express train south from Seoul, the biggest noise was provided by South Korean fighter jets roaring overhead in formation.
Raikkonen, who struggled with a bad back in Singapore two weeks ago, skidded hard into the tyre wall at the final corner in the closing seconds of the morning session but clambered out of the car without any apparent difficulty.
The 2007 world champion clocked the eighth best times in both sessions.
"Obviously it didn't help that I destroyed part of the car this morning; maybe I ran out of talent there," commented the Finn, whose car was quickly fixed.
Red Bull's Mark Webber, who will have a 10-place grid penalty on Sunday after collecting his third reprimand of the season for a Singapore post-race 'taxi ride' on Alonso's Ferrari, was third and fourth respectively.
Hamilton's team mate Nico Rosberg reinforced the idea that the battle lines were drawn between Mercedes and Red Bull with the fourth and third best times.
Vettel was in a league of his own on the streets of Singapore and there were suspicions on Friday, where teams can be running with different fuel levels, that the 26-year-old had plenty in reserve.
"In terms of competitiveness, all the usual Friday caveats apply: we know only what fuel loads we ran, not those of our competitors, so tomorrow will show us where we actually stand," said Mercedes principal Ross Brawn.
Marussia's Venezuelan test driver Rodolfo Gonzalez hit the wall early in the first session when he was almost alone on the circuit.
Britain's James Calado was also given time in the Force India, with compatriot and race regular Paul Di Resta sitting out the session before returning in the afternoon. (Reporting by Alan Baldwin; Editing by Pritha Sarkar)