Amazon.com may sell as many as 5 million tablet computers in the fourth quarter, making the largest Internet retailer the top competitor to Apple in this fast-growing niche of the consumer PC market, Forrester Research said yesterday.

Amazon.com has to price its tablet “significantly” below competing products and have enough supply to meet demand, but if the company can pull this off it can “easily” sell 3 million to 5 million units in the final three months of 2011, Forrester’s Sarah Rotman Epps predicted.