By Tommy Stubbington 

Greek stocks on Monday felt the weight of the success of antiausterity party Syriza in the country's election, but the impact on European markets more broadly was mild.

Athens' main stock index initially slumped by nearly 5%, and was still 2.5% lower by early afternoon. Bank shares were sharply lower, with Piraeus Bank SA down more than 11% at the bottom of the pan-European index. Peers Eurobank Ergasias SA and Alpha Bank AE were both more than 6% lower.

The victory for antiausterity party Syriza could set Athens on a collision cause with its creditors and embolden radical parties elsewhere to challenge Europe's economic orthodoxy. Analysts and investors said they had anticipated a victory for Syriza given the party's lead in the polls, but the size of the margin was something of a surprise.

Maria Paola Toschi, a market strategist at J.P. Morgan Asset Management, which looks after around $1.7 trillion globally, said that banks in Greece are "the biggest potential losers from the extended period of uncertainty that markets may be in for."

But weakness in the euro--which has already chalked up big losses this year--was short-lived, with the currency picking up against the dollar and the yen in European trade.

Wider equity markets in Europe were unruffled by the news, with stocks closing in on recent seven-year highs after a small early wobble. The Stoxx Europe 600 index was 0.1% higher. In the U.S, the S&P 500 is indicated opening 0.3% lower. Futures, however, do not always reflect moves after the opening bell.

Investors appear confident that the bond-buying stimulus program known as quantitative easing, announced last week by the European Central Bank leaves markets much less vulnerable to fears of a eurozone breakup than they were during previous episodes of the Greek crisis.

"Political risk is back on the radar in Europe, but markets are still under the influence of the ECB's liquidity injection," said François Savary, who oversees about $10 billion of assets as chief investment officer at Swiss bank Reyl.

"We expect that [ECB] backstops have effectively firewalled Greek developments and should limit contagion or re-emergence of [eurozone] existential anxiety. As such we don't expect developments to translate into substantial further euro weakness beyond what is already justified by QE," said currency strategists at BNP Paribas.

In Asian trading hours, the euro dipped to a fresh 11-year low to the dollar of just below $1.11. Ultrasafe German debt rallied to new all-time highs while bonds in fiscally weak eurozone countries declined.

The result gives Syriza "a strong mandate" to push through major changes to the Greek adjustment program, said Jan von Gerich, chief strategist at Nordea.

"The ensuing negotiations will be tough and contribute to market volatility in the coming months," he said.

Syriza's decision to strike a deal with the small Independent Greeks party could lead to more strained negotiations with Greece's creditors--given the two parties share little except a rejection of the austerity measures imposed on Greece by its creditors.

But yields--which rise as prices fall--remain below last week's highs.

Wider pressure on bond markets in the eurozone was modest on Monday.

Italian and Spanish 10-year yields rose slightly to 1.54% and 1.39%. Still, both countries' yields quickly fell back and remain within touching distance of the all-time lows hit in the wake of last Thursday's ECB meeting.

German yields, which typically fall in times of stress, touched a record low of below 0.3% on the 10-year bond before rising again to trade little-changed on the day.

Josie Cox contributed to this article

Write to Tommy Stubbington at tommy.stubbington@wsj.com

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