Apple sold 77.3 million iPhones in the final months of 2017, slightly fewer than during the same period in the prior year.
But higher prices compensated for the dip, lifting the firm's profits in the quarter to more than $20bn (£14bn).
The record results, which included strong growth in Japan, were the first to provide a glimpse of sales of the firm's expensive iPhone X.
Apple boss Tim Cook said iPhone X sales surpassed the firm's expectations.
Apple released the 10th anniversary phone, which starts at about $1,000, in November. It has been the top-selling phone every week since, Mr Cook said.
Investors had been worried that demand for the firm's products may be dimming.
The number of iPhones sold in the period slipped 1% year-on-year, but Apple executives said it was important to remember that the quarter was one week shorter than in 2016.
Quarterly revenue climbed 13% year-on-year to a record $88.3bn.
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