Padraig Harrington opened with a 4-under par 68 and took the early lead at the Texas Open on Thursday.
The former British Open and PGA Championship winner overcame the chilly early morning temperatures and steady wind to go as low as 5 under before finishing with a bogey on No. 18.
Rory McIlroy, who entered the tournament last week as a final opportunity to prep for next week's Masters, opened with an even-par 72. He was tied for 23rd with the morning rounds ongoing.
The former world No. 1 was 2 under early in his round, which began on No. 10 on the difficult 7,435-yard layout.
However, McIlroy found the water on the par-5 18th when his approach came up short - beginning a stretch of three straight bogeys.