VALENCIA, Spain - Sebastian Vettel was left frustrated after retiring from the lead during the European Grand Prix and losing vital ground in his chase for a third successive World championship.The Red Bull driver, who started frompole, dominated from the start when his engine failed on lap 35. He was forced to retire while team mate Mark Webber worked his way up to fourth despite starting near the back of the grid.The defending Drivers' champion had pulled out a comfortable lead and was in command before the pace car emerged midway through the race.'NOTHING WE COULD'VE DONE'Following the re-start, Vettel looked to have things back under control and was re-establishing his advantage before his engine stalled and he was forced to hand the lead to eventual race-winner Ferrari's Fernando Alonso.The Red Bull team was not sure what had caused the problem but suggested the pace car period may have had something to do with it.Vettel said: "The engine stalled, the engine switched off and there's nothing that we could have done. At the moment we don't know what the problem was. The pace car was obviously not ideal for us and it might be that the retirement in some regards is also down to the safety car so it's a shame."I think up to that point it was clear that we were very strong and I felt happy in the car. We had the pace and we were very, very quick today. I was surprised, it felt really good. Also after the safety car the initial restart was OK."Despite of this, Vettel was pleased with the improved pace of his car and believed he could have won the race.WEBBER TRUMPS VETTELVettel said. "It's OK. There is not much we could have done better today. It's just reliability. We all work on the limit and so does the car so, surely it's a shame, but I think up to that point we did everything right."Perfect pit stops, perfect start, perfect race. I think everybody has seen what would have happened."Webber started 19th but wound up fourth after retirements from drivers in front of him and some excellent overtaking during the race. He was delighted with the result and believed picking the right strategy was key to his success.He said: "Another crazy day. As we're finding out, it's very different to know what's going to happen on Sundays. Obviously there was a bit of attrition at the front today, with a Lotus, Lewis (Hamilton) and Seb (Vettel) as well. I'll take that."Strategy's all about rolling the dice and going on the fly, all the time. Trying to - not guess - but work out what's going on. In the end it's a lot of points for me so I'm happy with that from that grid position."