Pandora, the biggest Web radio service's market shares fell as much as 12 percent Monday after Apple announced that its newly launched iTunes Radio service attracted 11 million unique listeners since its debut along with the iOS7 mobile operating system.

Pandora, the biggest web radio service, has got itself a newest and by far the toughest competitor, Apple. The last weekend was the most promising for Apple with a record-breaking sale of nine-million iPhone 5S and 5C models and the new week kicked off with greater news that Apple's free Internet radio service, iTunes Radio has attracted 11 million unique listeners. As a result, Pandora saw its shares slide as much as 12 percent, Monday.

This has been a double win for the Cupertino based tech giant. Its shares even rose 5 percent to $490.64 after successful sales of its new iPhone devices. The new iTunes Radio service was introduced along with the iOS7 update. The service was launched alongside several new features in iOS7 such as Control Center, Notification Center, improved Multitasking, AirDrop and lot more.

While the strong debut of iTunes Radio seems promising, Michael Pachter of Wedbush Securities  begs to differ. "All the Apple stuff is pretty old news and should have been anticipated," Pachter said in a statement. "People are likely to check iTunes Radio out, but it is not going to be as good as Pandora for most, so [the stock decline] should be a transitory impact."

The successful debut of iTunes Radio is also partly thanks to the choice of music it offers. The tech giant said in a press release that the most listened song on iTunes Radio was "Hold On, We're Going Home" by Drake.

Pandora has a whopping 72 million active user-base and has seen great success before the debut of iTunes Radio. Its shares almost tripled on the year. The radio service company raised nearly $378.8 million toward financial growth and also sold 15.7 million shares for $25 each, Bloomberg reports.

Apple has also seen remarkable success with its new mobile operating system. The iOS7 was downloaded more than 200 million times besides the fact that it was on the 9 million iPhone 5S and 5C devices sold last weekend.