The Alternative for Germany (AfD) party, founded by a professor who believes the single European currency has been a disaster for Germany, scored five percent in the poll from independent institute INSA.
That figure is the bare minimum required for representation in the Bundestag lower house of parliament. Until now the AfD had been credited with around three to four percent.
Merkel's conservative Christian Democrats held steady in the polls at 38 percent, while their current coalition partner, the pro-business Free Democrats (FDP), gained two points to six percent.
Pollsters say that the entry of an AfD bloc in parliament would rob Merkel's coalition of a governing majority based on current estimates of its number of seats.
Such an outcome would most likely force her to form a left-right "grand coalition" with the Social Democrats (SPD), who scored 28 percent, up one point, in the latest poll.
Their preferred partner, the opposition Greens, tallied eight percent, putting a centre-left alliance under SPD candidate Peer Steinbrück out of reach.
The far-left party Die Linke reached nine percent, taking the total vote share of SPD, Greens and Linke to 45 percent, one point ahead of Merkel's Union-FDP bloc.
However, both the Social Democrats and the Greens have ruled them out as potential partners, making a red-red-green coalition unlikely.
The AfD has been labeled as populist in German media and garnered negative headlines for accounting irregularities and some members' reported far-right leanings.
Its main message is that bailout packages for debt-mired southern European countries have made the euro untenable for Germany and called for a return to the Deutschmark.
Talk of fresh aid to Greece during the election campaign has given the party a further boost, with eurosceptic Germans believing their country has paid multiple times for the economic mistakes of foreign governments.
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Meanwhile, the socially liberal, technology-focused Pirate Party dropped one point to two percent, a full three points below the share they would need to win seats in the Bundestag.
The INSA poll covered 2,248 people and lasted from Sunday September 15th to Wednesday September 18th.