Jimmy Walker opens up four-shot lead at Valero Texas Open

Jimmy Walker has built a four-stroke lead heading into the final round of the Valero Texas Open in San Antonio.

The US Ryder Cup player had a mixed start to his day, making two bogeys and three birdies to head into the back nine at one-under par for his round.

A further dropped shot at 12 left the 36-year-old on six-under par, but birdies at 14, 17 and 18 saw Walker reach the clubhouse four ahead of fellow American Jordan Spieth.

The winner appears likely to come from Walker or Spieth, with Billy Horschel in third place on the leaderboard, but languishing six shots off the pace.

On a tough day for scoring, only four of the top 16 players were able to break 70.