(Reuters) -Davis Cup heavyweights Australia and the United States eased through the first qualifying round on Saturday but Britain were knocked out as Japan hit back from 2-1 down to win 3-2, while Denmark staged a dramatic comeback to overcome Serbia.

Jacob Fearnley and Billy Harris both lost their singles matches on Saturday as Japan earned a 3-2 Davis Cup win over Great Britain in Miki, Japan to send Leon Smith's team to a relegation playoff.

Great Britain face a Davis Cup relegation play-off after losing their first-round tie 3-2 against Japan. With the tie level at 1-1 after Friday's opening day, Britain took the lead when Neal Skupski and Joe Salisbury won Saturday's opening rubber 7-6 7-6 against Yosuke Watanuki and Takeru Yuzuki.

Alex Michelsen gave the United States a 2-0 lead over Taiwan on his Davis Cup debut in the first round qualifiers on Friday, while Jacob Fearnley also impressed in his first appearance in the competition to pull Britain level with Japan.

Japan fought back from 2-1 down to beat Britain 3-2 in their Davis Cup qualifier on Saturday to advance to the second round while the United States sealed a 4-0 victory over Taiwan.