OBERHOF, Germany – Oh, it’s on. The battle between Marit Bjørgen (NOR) and Justyna Kowalczyk (POL) for Tour de Ski queendom has officially begun—with Kowalczyk landing the first blow. By a scant 0.4 seconds, the Polish strongwoman claimed victory in the first stage of this year’s Tour on Thursday afternoon, covering the icy 3.1-kilometer freestyle prologue in just over seven minutes. Bjoergen was second, with 21-year-old Swede Hanna Brodin earning her second-ever World Cup podium...