As Americans went to the polls, the peso opened at 18.95 per dollar, down 0.53 percent from Monday's closing price of 18.85, according to private bank Banamex.
The Mexican stock market, however, rose 0.2 percent in early trading.
The national currency has had a roller-coaster ride during the US presidential campaign, falling when Trump was up in opinion polls and rising when Democratic presidential nominee Hillary Clinton fared better.
The peso tumbled to 19.50 per dollar last week when a poll put the Republican real estate tycoon ahead of Clinton.
But the Mexican currency and stock market surged Monday, a day after the FBI confirmed Clinton would not be prosecuted for using her private email server for government communications when she was secretary of state.
Analysts say Mexico's economy could suffer under a Trump presidency because of his vow to renegotiate a free-trade deal, block remittances sent by migrants to their homeland and make the neighboring country pay billions for a massive border wall.