Apple's launch of the iPad Mini hit the company's sales figures in the previous months as users hung on for the new device.
After high sales figures in the second quarter, shipments slowed in the third, leading to gains for Android, says IDC in a report.
Apple's market share slid from 65.5 percent to 50.4 percent for the quarter.
"After a very strong second quarter, Apple saw growth slow as both consumer and commercial (including education) shipments declined, and rumors of a forthcoming iPad mini began to heat up," says Tom Mainelli, research director for tablets at IDC.
"Now that the new mini, and a fourth-generation full-sized iPad, are both shipping we expect Apple to have a very good quarter. However, we believe the mini's relatively high $329 starting price leaves plenty of room for Android vendors to build upon the success they achieved in the third quarter."
Showing the most impressive growth, thanks to the Galaxy Tab and Note 10.1, was Samsung, which shipped 5.1 million tablets worldwide in the third quarter. This was up 115 percent on the previous quarter, and 325 percent up on last year.
"Samsung took advantage of an opportunity in the second quarter. The company offers a wide range of tablet offerings across multiple screen sizes and colors, and that clearly resonated with more buyers this quarter," says Ryan Reith, program manager for IDC's Mobile Device Trackers.
"Its growth to 18.4 percent of worldwide market share during the quarter represents the first time a competitor has attained this level of share since the original launch of the iPad."
The top five was rounded out by Amazon, Asus and Lenovo.
"Competitors are turning up the pressure on market leader Apple. With the recent introduction of a number of Windows 8 and Windows RT tablets, consumers now have a third viable tablet platform from which to choose," says Reith.
"However, price points are critical in tablets, and Microsoft and its partners will have a tough time winning a share of consumer wallet with price points starting at $500."
Overall, the tablet market showed strong growth, up 49.5 percent year on year and 6.7 percent up on the previous quarter.