Store owner Andrew Spence said the couple "had no idea" they'd won.
"It was a 'can you please check my last week's ticket?' and they were told they were the winners," he said.
Spence said a prize claim form, bottle of champagne and a chair was on standby since the draw last Saturday.
"All three were ready just in case the winner was someone who was completely unaware they'd won and it seems like it was the case, so all three things were put into place right away," he added.
"We were on edge each time someone came in and asked us to check their tickets."
The couple are one of four recent Lotto winners in Napier, with two of the city's residents taking home $142,857 each in Lotto's First Division two weeks ago.
Those tickets were sold at Tamatea Pak 'n Save and Paper Plus Taradale.
A fellow Napier resident also won big in last Wednesday night's draw, taking home $1m.
That ticket, which was one of nearly 1.6 million sold across the country, was sold at Napier City Pak 'n Save.
The pharmacy, on Maadi Rd, has seen a rise in visitors to the store as a result, according to Spence.
"It put a lovely end to what had been an exciting week," he said.
"We've been rather popular, with lots of people not even necessarily coming to buy a ticket, just to look at the store. It's been a bit of a tourist destination."
While the $50m prize wasn't struck, six players from Auckland and one from Tauranga, Palmerston North and Invercargill each won $5.02m in Lotto Second Division after there were no First Division winners.
All 10 have now come forward.
Further details of the winning couple have not yet been released.
