Le Pen, leader of the National Front, campaigned on a threat to dump the euro and pull France out of the European Union.
Losing its second biggest member could spell the end of the eurozone, and tip the region into recession, economists had warned before the vote.
Analysts say the fact that opinion polls had consistently predicted a Macron-Le Pen run-off could boost market confidence because the polls suggest Macron should win easily in a second round.
"That's what the foreign exchange market is going to trade off in the days ahead and indeed is already doing," said Kit Juckes, strategist at Societe Generale.
euro dollar chart france election
Macron has already won pledges of support from two defeated rivals -- center right candidate Francois Fillon and Benoit Hamon, the candidate of outgoing President Francois Hollande's Socialist Party. Together Fillon and Hamon won about 25% of the vote in Sunday's first round.
That mainstream backing could be crucial for Macron in the second round of the election, given he is running without the support of an established political party.
And assuming he wins the presidency on May 7, he will need broad support in the French parliament to turn his policy promises into legislation.

"Chances are that France will get the economic reforms it needs to revive its fortunes and catch up with Germany," said Holger Schmieding, chief economist at Berenberg bank. Europe could benefit too from a renewed effort by France and Germany to strengthen the cohesion of the eurozone, he added.
Macron has promised to cut corporate tax rates gradually to 25% from the current 33%. He also wants to make France's 35-hour work week more flexible, and slash housing taxes for most people.

What to know about Emmanuel Macron
He has pledged to cut public spending by €60 billion ($64 billion) a year, and plans an economic stimulus package worth €50 billion over five years.
Macron is a free trade supporter and campaigned in favor of the EU's new agreement with Canada.