Slow start. Big first set rally. Win and advance. That was Serena Williams in the second round of the U.S. Open Tennis Championship Wednesday afternoon.

Williams struggled with 23-year-old Kiki Berterns of the Netherlands but won in straight sets 7-6, 6-3.

So Williams quest for the 2015 tennis grand slam continues...on Friday vs fellow American Bethanie Mattek-Sands.