Great Britain's James Ward lost in straight sets to Dusan Lajovic as Serbia drew level at 1-1 in the Davis Cup quarter-final in Belgrade.
Ward lost 6-1 6-3 6-2 in one hour and 52 minutes against a player ranked 159 places above him, at 81st in the world.
Kyle Edmund gave Great Britain the lead on Friday with a straight-sets victory over Janko Tipsarevic.
Jamie Murray and Dom Inglot will face Filip Krajinovic and Nenad Zimonjic in the doubles later on Saturday.
Great Britain are defending the Davis Cup title they won in Belgium last year.