Masson, who has made the cut just once in her first season on the tour, finished 36 holes at the Las Colinas Country Club with a 7-under 135 total.
She had a one-shot lead over Carlota Ciganda, who reached 136 with a round of 70.
Moriya Jutanugarn, Kathleen Ekey and world No. 1 Inbee Park were all at 137 in a tie for third. Jutanugarn produced the day's lowest round of 66.
Although she is in her first year on the LPGA circuit, Masson has spent three seasons on the Ladies European Tour. She has one won once in Europe.