In 1999, Mattek played her first WTA Tour event in Philadelphia where she received a wildcard into the qualifying. She lost in the first round of qualifying to Nana Miyagi. It was the only tour match of the year for Mattek. Then in 2000, Mattek received a wildcard into qualifying at the Lipton International Players Championships in Key Biscayne, Florida but lost in the first round to Anca Barna. Later in the year, Mattek played in her first Grand Slam event at the US Open. She was given a wildcard into the qualification rounds, but lost in the first round to Gisela Rivera.