Vandeweghe has won both their previous matches. Their last meeting was in June 2014 on grass. She won in 3 sets. Both her wins were on grass.
Muguruza has struggled to get her game back on track after she won the French Open in May. She reached the third round in Rio but won just 2 games against eventual champion Puig.
Vandeweghe has better hard court stats but if Muguruza plays her best tennis she wins. I think that may not happen today and will lay Muguruza below 1.30