Research giant Gartner had a quick lesson for Apple: don’t let off the iPhone accelerator — if you do, you’ll pay. The latest price for delaying until October its new smartphone: iOS dipped to 15 percent of sales while Android-based handsets skyrocketed to 52.5 percent of the market.

The delay of the iPhone 5, when eventually morphed into the iPhone 4S, gave Android smartphones a three-month period to grab market attention, propelling the Google mobile operating system from 25.3 percent in the third-quarter of 2010 to more than 52 percent in the same period this year, the research firm announced. Meanwhile, Apple’s iOS slipped from 16.6 percent of the market in the third-quarter of 2010 to 15 percent of sales during the same period this year.

Apple’s slip was due to consumers “waiting for a rumored new iPhone and associated price cuts on older iPhone models; this affected U.S. sales particularly,” writes principal research analyst Roberta Cozza.

But Apple is not likely to see a similar decline during the fourth quarter. “Gartner believes Apple will bounce back in the fourth quarter because of its strongest ever preorders for the iPhone 4S in the first weekend after its announcement,” Cozza adds. Emerging markets, such as Brazil, Mexico, Russia and China “are becoming more important to Apple,” amounting to 16 percent of overall iPhone sales.

Although Nokia remained the top seller of mobile phones, its global market share again slipped, dropping to 23.9 percent from 28.2 percent of the market. Apple increased its share of worldwide cell phone sales to 3.9 percent from 3.2 percent in 2010. Samsung slightly increased its share of the cell phone market, growing to 17.8 percent, up from 17.2 percent during the third-quarter of 2010.

If Apple took it on the chin in smartphones, it turned an otherwise slumping PC market into a positive. Apple saw Mac sales rise 7.6 percent during the third-quarter, selling 1.13 million computers for 7.6 percent of the Western European market, Gartner said.

In an otherwise down cellphone global market, only Apple and Android-backer Samsung