Upon checking my earlier diaries and sources, some correction: before the first round, it was right-wing candidate Lourdes Flores Nano who consistently beat Humala in a hypothetical runoff vote in opinion polls; but between the two rounds, García beat Humala in every poll. Interestingly, it was García who most vehemently protested poll results, and that for favoring Lourdes over him.

Note that in the first round, the two main candidates acceptable to Washington got 48.1% together vs. Humala's 30.6%, with two more ex-Fujimori right-wingers getting another 12.2%, which is beyond the margin of disputed ballots, and which makes the relative narrowness of Ollanta Humala's second-round defeat (given that voting is compulsory) the more impressive. (BTW, he himself conceded, while Lourdes Flores wouldn't concede her third place in the first round for almost a month.)

So all in all, I'd say: to give a different result, the scale of the needed vote tampering would be so large that it would have been more than enough for the US to propel Lourdes Flores not only into second but first place in the first round. On the other hand, the US could well have had a role in the campaign, and that while betting on multiple horses in the race.

_{*Lunatic*, n.
One whose delusions are out of fashion.}