Samsung's first quarter profits fell by 39% as mobile customers switched to the new big-screen iPhones.
Earnings from the South Korean firm's mobile business have been squeezed to less than half what they were a year earlier.
The company reported that its January to March profit was £2.8bn - down from £4.5bn. The figure is lower than analysts forecast.
Until the launch of Apple's iPhone 6 and 6 Plus, large screens were one of the features that set Samsung apart. But since the launch of Apple's new device last autumn, Samsung has taken a hit.
While the company still sold more smartphones than Apple during the quarter, many of them were at the lower-end of the market with a smaller profit margin.
Apple sold 61 million iPhones in the first three months of the year, an increase of 40% from a year earlier, which drove another quarter of big profits.
Samsung, which does not disclose its smartphone shipments, is estimated to have sold 83 million smartphones during the quarter. The Korean company said its profits would increase during the second quarter as the Galaxy S6 - and the S6 Edge with a curved screen - expand sales after their launch this month.
Sales of the iPhone have been growing in markets that Samsung typically dominates, such as in South Korea and Vietnam.
