The INSA poll for Bild daily released on Thursday (19 September) put Merkel's conservatives on 38% and the Liberal FDP party on 6%, giving a combined total of 44% - one percentage point lower than the total for the three left-of-centre parties.
The poll, conducted after last Sunday's state election in Bavaria, gave the eurosceptic Alternative for Germany (AfD) 5%, the amount needed to enter the Bundestag lower house.
It put the opposition Social Democrats (SPD) on 28%, the Greens 8% and the hardline Left 9%.
Schäuble lashes out at AfD
The AfD's rapid rise in opinion polls pushed Angela Merkel's conservatives to switch tactics ahead of Sunday's vote, in a bid to defend their majority in the Bundestag, the German parliament.
Merkel's Christian Democrats (CDU), which had deliberately ignored the small AfD party so far in the campaign, deployed one of their most respected figures – Finance Minister Wolfgang Schäuble – to rip into the new anti-euro party.
"These people claim 'We'd be better off economically without the euro'," the minister, celebrating his 71st birthday, told the weekly Die Zeit. "That claim is totally wrong, has no credibility and is extremely dangerous for our prosperity."
The AfD, created in February, has up to 4% support in opinion polls. If it clears the 5% threshold for entering parliament in the September 22 vote, it could rob Merkel of any chance of securing another centre-right majority.
While Merkel's conservatives are almost certain to come first and win her a third term, two recent polls have put her coalition a point behind the combined opposition.
'Grand coalition' looking more likely
If the conservatives and pro-business Free Democrats (FDP) do not win a majority, she may be forced into a 'grand coalition' with the centre-left Social Democrats (SPD), which could take a softer line towards struggling southern eurozone countries.
"The final phase of the German election campaign has not gone well for Chancellor Merkel," wrote Holger Schmieding, chief economist of Berenberg Bank, in a research note. "Momentum has turned slightly against her centre-right coalition."
The closely watched Allensbach poll for the conservative Frankfurter Allgemeine Zeitung daily, out on Wednesday, showed the conservatives down a point at 39% and the FDP steady at 6%, giving the centre-right 45%.
The combined opposition was 1 point ahead, with the SPD up a point at 26%, their Greens partners at 11% and the hardline Left at 9%. Because the SPD and Greens rule out a coalition with the Left, the most likely scenario is a repeat of the 'grand coalition' that Merkel led between 2005 and 2009.
Merkel said she aimed to continue her coalition with the FDP no matter how tight the result might be.
"The majority is very often small in Germany," she said in an interview with public TV channel ARD aired later on Wednesday.
"If citizens give us a mandate to continue the current coalition,... we will take the responsibility to govern together, no matter how big [the majority] is."
"It's still completely open which coalition will rule," said Renate Köcher, head of Allensbach.
Merkel's conservatives have long been wary of opinion polls after having seen their election results drop below final voter survey forecasts in the last six elections.
Recent polls do not fully reflect the potential boost to Merkel from last Sunday's state election in Bavaria, where the CDU's conservative sister party, the Christian Social Union, won a landslide victory.
"It's conceivable the strong Bavaria win may help the conservatives. It's going to be extremely tense on Sunday," Forsa director Manfred Güllner told Reuters.
He said the outcome could be especially clouded by the AfD. Its entry would mean the centre-right would need at least 47% to win a majority in parliament - seen as unlikely.
Riding a tailwind, the AfD said it got €430,000 in donations from 6,000 people in 48 hours after an online appeal for support at the weekend. The AfD's TV campaign ad was viewed by one million viewers on YouTube, the party said.
Pollsters, analysts and politicians have expressed concerns that support for the AfD, popular on the far right because of its tough stance on immigration, could be even higher as its supporters might conceal their true intentions from pollsters.
"I don't have any time for these people who seem to be trapped in the past," Schäuble told Die Zeit, breaking with the CDU's strategy of ignoring the AfD in a sign of nervousness in the Merkel camp.
Schäuble predicted they would soon fade away as had other "single issue, backwards-looking little groups" in the past.