It happened as fast as it takes to download a new app for the iPad.

Sije Pederson was standing near 22nd and Mission streets at around 7:30 p.m. Sunday, when a thief jerked the MacBook Pro box out of her hands and started to run north on Mission Street.

The 30-something from Norway ran after the mugger, grabbed the box that held her Mac – one she had purchased only an hour earlier in downtown San Francisco – and tussled with the thief, she said.

“He was starting to yell, I tried to pull it from him, then he pulled it,” she told police who arrived 20 minutes after the attack.

She fell as the mugger tried to twist the box away from her, she said. “I dropped it and then he dropped it as well,” she said.

Sije Pederson and a friend as they talk to police.

Pederson told police that she thinks the mugger realized that another young man had noticed what was happening and had started to run after him.

The thief took off, and turned east on 21st street, she said. “I lost him,” said the young helper, who declined to give his name. “He was just another drugged out” guy.

The suspect was wearing black jeans and a black hoodie with a yellow patch, the witness said.

Pederson said she was worried that her computer was damaged. She leaves tomorrow for Mexico.

Correction: An earlier version of the story reported that it was an iPad, but a reader wrote in saying it was a MacBook Pro and a comparison between the two boxes says that the reader was right.