Hamilton controlled the race from the start after converting his
into a lead at the first corner, but retired on lap 23, handing the lead and eventual victory to Vettel.
"It was gutting when the car stopped; I was cruising," Hamilton said. "I was managing the gap and could have pushed more, I had the pace. I think today would have been an easy win.
"Nonetheless, that's not the case. The Red Bulls did a good job, Jenson too. We've got six races left and I need to keep pushing. I need to win the rest of them.
"It's just heart-crushing when you know you have 25 points easily if you don't have any problems, and then the problem came."
McLaren's Lewis Hamilton retires from lead
McLaren team prinicpal Martin Whitmarsh said there had been no indication before the race that there was anything wrong with McLaren's gearbox and said he did not think an incident in qualifying in which Hamilton brushed the wall would have caused enough damage to contribute to it.
"It was a very light tap," Whitmarsh said. "This morning we saw the wheel had some paint rubbed off and some paint from the wall, but a very small section, the rim wasn't damaged, the tyre wasn't damaged.
"In fact I was nagging the engineers to check track and camber and they did but it was such a light touch they don't think it was [too damaging]."
Vettel's victory, his second of the year, puts him in an apparently strong position in a faster car than the Ferrari.
"It looks better than before," Vettel said. "Fernando finished third. I am not a genius but I think it is looking 10 points better than before.
“Of the four of five contenders, we lost points with one, with the other three we increased our advantage”
"There's a lot of races left and it's a bit difficult to predict what's going to happen. We have to make sure we finish the races first of all.
"I think the pace is there, even if we are not quick enough to win then it is good enough to collect a lot of points, and we have to make sure we do that.
"It is a tough championship so far but we're still in it. We're looking forward to the next couple of races and obviously the target at the moment is to beat Fernando."
Alonso said: "In Monza [at the last race], it was Lewis winning the race and Sebastian retired. Here it is Sebastian winning and Lewis retiring. So for me it is OK if they keep doing it like this.
"I think it's a very positive weekend. A very good weekend. Of the four of five contenders, we lost points with one, with the other three we increased our advantage.
"So when we are not quick enough, to win more points against three of our opponents, I think it's positive."
Singapore Grand Prix 2012, day three
Sunday, 23 September: Highlights on BBC Three at 19:00 BST.
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