Analyst firm IDC today reported that makers of tablets running the Android mobile operating system, including Samsung and Amazon, had 'gained momentum' over Apple's iPad over the three month period.
Worldwide shipments of tablets hit 27.8 million units in the quarter, and Apple commanded a 50.4% share of this total.
The US firm shipped 14m iPads in the quarter, up from 11m in the same period in 2011, but its share was down from 59.7% in that period.
Apple's market share had also fallen from 65.5% in the second quarter of 2012, as rivals managed to catch up with the firm.
IDC noted that the third quarter was marked by a 'surge' in shipments for the major Android tablet makers, Samsung and Amazon.
Samsung cemented its position as the second biggest tablet brand, with an 18.4% share of shipments, up from just 6.5% in the same period a year ago.
The Korean firm shipped 5.1m of its Galaxy Tab slates in the third quarter, up from just 1.2m in the 2011 period, although it is important to note that this is just shipments, and not sales.
According to IDC, Amazon.com shipped 2.5 million of its 7-inch and 8.9-inch Kindle Fire tablets in the third quarter and now has 9% of the global market.
Asus, maker of Google's Nexus 7 amongst other tablet products, shipped 2.4m slates over the three months, up from just 700,000 in the same period last year.
Thanks largely to the Nexus 7, the Taiwanese firm's market share has increased to 8.6% from just 3.8% in Q3 2011. The top five was rounded out by Lenovo with a 1.4% share, mostly in China.
Ryan Reith, programme manager at IDC's Mobile Device Trackers, said that Samsung has managed to appeal to consumers in the iPad-dominated tablet market.
"The company offers a wide range of tablet offerings across multiple screen sizes and colours, and that clearly resonated with more buyers this quarter," he said.
"Its growth to 18.4% 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."
Reith said that competitors are now putting significant pressure on market leader Apple, including Android slates and also the arrival of new products running Microsoft's Windows 8.
"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," he said.
"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."
Apple has already noted that the anticipation ahead of the launch of the fourth-gen iPad and new iPad Mini last month resulted in a slowdown in iPad sales in the third quarter.
But Tom Mainelli, the research director for tablets at IDC, said that they expect Apple to have a "very good" final quarter in 2012 with its new products on the shelves.
"After a very strong second quarter, Apple saw growth slow as both consumer and commercial (including education) shipments declined, and rumours of a forthcoming iPad mini began to heat up," he said.
"We believe a sizeable percentage of consumers interested in buying an Apple tablet sat out the third quarter in anticipation of an announcement about the new iPad mini.
"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, Mainelli noted that the "relatively high" starting price of £256 for the iPad Mini "leaves plenty of room for Android vendors to build upon the success they achieved in the third quarter".
Over, the tablet market grew 49.5% year-over-year in third quarter and 6.7% over the second quarter of 2012.
Today, Apple announced that it sold 3m iPads over the weekend following the launch of the iPad Mini and fourth-generation iPad.