AUGUSTA — Defending champion Jordan Spieth began a strong defense of his Masters title with a 6-under par round of 33-33—66 Thursday at Augusta National Golf Club as he attempts to become the first back-to-back champion since Tiger Woods (2001-2002).

On a sunny but blustery day with wind whipping at around 20 mph, Spieth birdied Nos. 3, 6, 8, 10, 13 and 18 to take an early two-shot lead over Shane Lowry, who was 4-under after five holes with birdies on holes 2-5, and pre-tournament favorite Jason Day, who was 4-under after eight holes. Day was ranked No. 1 entering the tournament.

Englishman Paul Casey, playing in the same group with Spieth, shot a 3-under 69.