Ukraine are in pole position with 10 points from four games, followed by Luxembourg who have four points from as many matches. Third-placed Serbia are on four points from three games and trail Luxembourg on goal difference.
European champions Portugal, who won the Nations League on Sunday with a 1-0 win over Netherlands, have two points from two games and Lithuania prop the group with one from three.
Having suffered a 5-0 drubbing in Ukraine on Friday, Serbia celebrated their first win of the campaign behind closed doors as they served a one-match crowd ban for fan misbehaviour in their Nations League match against Montenegro in November.
Two clinical goals by Aleksandar Mitrovic and a superb strike by Real Madrid's new signing Luka Jovic gave Serbia a 3-0 first-half lead and Adem Ljajic sealed the rout after Arvydas Novikovas had netted a 71st-minute penalty for Lithuania.
Ukraine were made to work hard for their win against Luxembourg and endured several scary moments after striker Roman Yaremchuk scored the game's solitary goal with a sixth-minute header from Ruslan Malinovskyi's cross.
