Thompson's first LPGA tournament in 2011 was the Avnet LPGA Classic, with a sponsor's exemption. After three rounds, she was tied for the lead with Song-Hee Kim. On Sunday, her score soared to 78, including back-to-back double bogeys on the 14th and 15th holes. Thompson finished tied for 19th at −1 (71-71-67-78=287), nine strokes behind the winner, Maria Hjorth. She missed the cut at the ShopRite LPGA Classic, at the LPGA Championship and at the U.S. Women's Open and tried but failed to Monday-qualify at the State Farm Classic. In her fifth LPGA tournament she played in 2011, the Evian Masters, she finished tied for 36th. She continued to play regularly on the Fuzion Tour, through the spring and summer. In August, she finished T31 at the Safeway Classic and then missed the cut at the Canadian Women's Open. In September, she won her first LPGA tournament, the Navistar LPGA Classic, by a five-stroke margin over LPGA Tour rookie Tiffany Joh. At age sixteen, she became the youngest winner ever on the LPGA Tour, breaking the previous record set by Marlene Hagge at age 18 in 1952. Her record stood for 11 months until 15-year-old Lydia Ko won the 2012 CN Canadian Women's Open on August 26, 2012.