Samsung had 20.8 percent market share in the first quarter of 2017. In Q1 2018, its 20.5 percent share was followed by Apple (14.1 percent), Huawei (10.5 percent), Xiaomi (7.4 percent), and Oppo (7.3 percent) respectively.
According to Gartner, global sales of smartphones to end users returned to growth in the first quarter with a 1.3 percent increase over the same period last year.
Nearly 384 million smartphones were sold in the first quarter of 2018, representing 84 percent of total mobile phones sold.
Xiaomi was the clear winner of the first quarter, achieving a growth of 124 percent year on year, the report showed. A refreshed portfolio of smartphones and aggressive pricing strategy helped Xiaomi hold the fourth position in the first quarter of 2018.
"This strategy led Xiaomi to achieve 330 percent growth in the Emerging Asia/Pacific region," said Anshul Gupta, Research Director at Gartner.
Samsung's smartphone growth rate will remain under pressure through 2018, with Chinese brand's growing dominance and expansion into Europe and Latin America markets, according to Gartner.
Samsung is challenged to raise the average selling price (ASP) of its smartphones, while facing increasing competition from Chinese brands that are taking more market share, the research indicated.
Apple's smartphone unit sales returned to growth in the first quarter of 2018, with an increase of four percent year on year.
"Even though demand for Apple's iPhone X exceeded that of iPhone 8 and iPhone 8 Plus, the vendor struggled to drive significant smartphone replacements, which led to slower-than-expected growth in the first quarter of 2018," Gupta noted.
"With its exclusive focus on premium smartphones, Apple needs to significantly raise the overall experience of its next-generation iPhones to trigger replacements and lead to solid growth in the near future," he added.
Huawei's refreshed smartphone portfolio helped strengthen its no. 3 global smartphone vendor position.
"Achieving 18.3 percent growth in the first quarter of 2018 helped Huawei close the gap with Apple," Gupta pointed out.
The results showed that Samsung's mid-tier smartphones faced continued competition from Chinese brands which led to its unit sales contraction year on year.