Serena Williams has lost the battle of mothers at the US Open in the semi finals to Belarus' Victoria Azarenka. 

The third seeded Williams went down fighting to Azarenka -- 6-1, 3-6, 3-6. 

The hunt for Williams' 24th Grand Slam title will continue. 

Meanwhile, Azarenka will now play Naomi Osaka for the finals on Saturday.