The new iPhone 5S and iPhone 5 made Apple the US top smartphone seller in September, despite their only being on sale for 10 days of the month.
New data from Counterpoint Research provided exclusively to the Guardian shows that Apple sold 4.8m phones there in September, jumping to a 38% share of the entire US smartphone market for the month. The figures include sales of the new iPhone 5S and 5C, which went on sale there on 20 September.
The competition saw Samsung drop to overall second place after having led the market since May.
Individually, the 5S was the best-selling phone, while the Samsung Galaxy S4 was the second best-selling. The cheaper 5C was in third spot.
But together, the two companies dominate the US smartphone business. Data from Counterpoint research shows that of the 68.1m smartphones sold in the US from April, 41.9m - or 61% - came from the two companies. Samsung is ahead of Apple, having sold 23.4m phones there in that period, against 18.5m for Apple.
That balance however is expected to change as more buyers seek out the iPhone. Separate data from ComScore suggests that growth in the total number of Android owners in the US has slowed over the summer, while that for Apple has held steady. The introduction of the new iPhones is expected to accelerate that.
However the cheaper iPhone 5C has not proved hugely popular with buyers so far, said Peter Richardson, research director at Counterpoint. "In general it seems that the 5C has been overshadowed by the 5S," he said. "The nature of the iPhone buyer is that they seem to be willing to pay for the best experience. The 5C is still regarded as slightly downmarket."
Separate data from Mixpanel, which monitors apps and other usage, suggests that the 5S is outselling the 5C by just under 4:1 on a global scale.
Richardson said that the top-end Samsung Galaxy S4, launched in May, "did well initially but as with a lot of Samsung products, it burned brightly but briefly." He says Samsung had big expectations about how many handsets it would sell but it underperformed: "if you're in the supply chain for the S4, the order book is closing down."
Apple tends to sell strongly in the US around Christmas, which has been timed around the release of phones over the past three years.
Among other Android brands, Counterpoint said that none fared well. LG's share fell below 10% of total sales despite launching its G2 model. Motorola increased its share slightly, to around 5%,while HTC's fell to around 3%.
Nokia's share was lower than HTC's, according to Counterpoint, suggesting that it sold fewer than 400,000 phones in the US during September. For the quarter, Counterpoint's data suggests that Nokia sold fewer than 1.5m phones in the US.
