Cameron Diaz & Ashlee Simpson: US Open Tennis Fans!

Cameron Diaz and Ashlee Simpson share lots of laughs while watching the US Open tennis tournament at the Billie Jean King Tennis Center in Queens, New York City on Monday (September 6).

The girls watched five-time champion Roger Federer beat 13th-seeded Jurgen Melzer of Austria 6-3, 7-6 (4), 6-3 Monday night to reach the quarterfinals.

Later today, Ashlee will be dressed in her sister’s Jessica Simpson Collection! Pete Wentz is also in town with their adorable son, Bronx, 21 months, pictured here.

UPDATE: Cameron was there was her rumored boyfriend, Alex Rodriguez!

FYI: Cameron is wearing Jennifer Meyer Jewelry Thin Gold Bangles with Stones. Ashlee & Pete are using their Maclaren stroller.

10+ pictures inside of US Open fans Cameron Diaz and Ashlee Simpson…