SHANGHAI (AFP) - World championship leader Sebastian Vettel set the pace in practice for the Chinese Grand Prix, topping the timesheets in both sessions in Shanghai on Friday in his speedy Red Bull. The 23-year-old German, the reigning world champion, has been the dominant force in the opening two races of the year, winning in Australia and Malaysia from pole position. He again stayed ahead of the field at the Shanghai International Circuit, leading Australian teammate Mark Webber by six-tenths of a second in morning practice. While Briton Lewis Hamilton was within 0.166secs of Vettel in the afternoon session for McLaren, Vettel still finished with the fastest lap of the day with a time of 1min 37.688secs. Vettel, who took Red Bull's first win as a constructor in China in 2009, said: "We found a good rhythm and we're happy with the car. "There's still a lot to do and I think it will be tight tomorrow and on Sunday, so we'll look where we can improve. "Today we had no big issues, but it's only Friday and so it's early in the race weekend." After disappointing results in the opening two races of the season, Webber again struggled to keep up with Vettel's searing pace. He was once more struck with reliability problems after his Kinetic Energy Recovery System (KERS) failed to work at all in last Sunday's Malaysian Grand Prix. The 34-year-old Australian was told by his team not to use the power-boost device in opening practice in China because of concerns over its reliability, while in the second session, Webber could only finish 10th and 1.639secs behind his teammate after a difficult run with the softer Pirelli tyre. Webber said: "Generally, it was a good Friday (but) I didn't have the best P2 (second practice), particularly on the short run with the new tyres, which is why my time is down a little. "The long run on the option tyre was good. We'll look at KERS tonight -- we'd like to run it this weekend." Webber sits in fourth place in the championship race, 28 points behind his teammate after the opening two races. Ferrari's two-time world champion Fernando Alonso was another dogged by technical issues and spent much of the afternoon sidelined by a hydraulics problem. But the Spaniard emerged late in the second practice session to finish 14th fastest, more than two seconds off the pace as the famed Italian team continued to struggle. A third and final practice session will take place on Saturday morning ahead of qualifying in the afternoon.