Japan has revised annualized gross domestic product (GDP) growth for January-to-March to 4.1 percent from a preliminary reading of 3.5 percent, official data showed on Monday.
A Reuters poll was expecting the growth figure to come in unchanged at 3.5 percent.
Quarter-on-quarter growth was revised upwards to 1 percent, compared to a preliminary reading of 0.9 percent. Economists polled by Reuters had expected no change from the initial reading.
According to Ed Rogers, CEO & CIO, Rogers Investment Advisors, the data add further evidence that the government's radical stimulus program is bearing fruit.
"Clearly, there's a lot more confidence back in this economy," said Rogers. "People are spending more money, that's the only way we would see this sort of GDP growth."
The data spurred a rally in Japanese stocks on Monday. The Nikkei jumped 3.5 percent at the open, after falling 6 percent last week, as markets questioned the effectiveness of Prime Minister Shinzo Abe's ambitious plans to end the economy's two-decade slump.
Still, some economists say it's too early to reach a verdict on Abe's economic policies, widely known as "Abenomics."
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"We have a lot of expectations built in here but if we don't see the light of structural reforms, 'Abenomics' will make things worse: printing more money, and higher debt levels, so we really need the reforms to come through at the end of the day," said Frederic Neumann, MD & Co-Head of Asian Economics Research at HSBC.
Rogers added a note of caution over over an overly euphoric market. The Nikkei was up more than 75 percent between mid-November and May, before the market succumbed to profit taking, briefly falling into bear market territory late last week.
"One of the biggest risks we've seen so far is that expectations will dramatically outpace the restructuring," he said. "The restructuring that needs to take place will take place over a 6 month to 24 month period. Looking at results within a 1 to 2 month period will create lots of frustration."
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Separate data out on Monday showed Japan's current account surplus doubling in April. This means the economy has logged a surplus for a third straight month, indicating that a moderate pickup in exports and huge income gains helped the nation's balance of payments.
The current account surplus stood at 750 billion yen ($7.70 billion), up 100.8 percent from a year earlier and much bigger than a median market forecast of a 320 billion yen surplus, according to data from the Ministry of Finance.
(Reuters contributed to this report.)