Updated

Mesa, AZ (SportsNetwork.com) - Hannah O'Sullivan, a 16-year-old amateur, closed with a 3-under 69 on Sunday to win the Gateway Classic, the Symetra Tour season-opener.

O'Sullivan finished at 15-under-par 201. She became the youngest winner in tour history and became the first amateur to win on tour since 1999. Cristie Kerr, who won on the Symetra Tour at the age of 17, owned the old record for youngest winner.

O'Sullivan got off to a quick start with birdies at one and three. She dropped in back-to-back birdies at seven and eight to move to minus-16.

The teenager was seven strokes clear of the field at that point. O'Sullivan parred six in a row from the ninth. She tripped to a bogey at the 15th, but parred the final three holes to earn the 4-stroke win.

Haley Italia also finished with a 3-under 69 to take second at minus-11. Giulia Molinaro matched the low round of the day with her 5-under 67. That helped her jump into third place at 8-under-par 208.

Two-time LPGA Tour winner Jimin Kang carded a 2-under 70 on Sunday. She headlined a group of 10 players tied for fourth at 6-under-par 210.