Zach Johnson joined fellow American Andrew Landry to tie for the lead ahead of the final day of the Valero Texas Open in San Antonio.

With back-to-back birdies on the 14th and 15th and another on the par-5 18th, Johnson shot a four-under 68 to join Landry, who carded 67, at the top on 13 under for the tournament.

Hot on their heels is record-setting Trey Mullinax, who pulled off a blistering round of 62 with two eagles and seven birdies to surge into third.

The 25-year-old's 10-under-par feat saw a dropped shot on the par-four 11th more than compensated by a hoard of birdies and eagles on the par five 14th and 18th, bringing him to within a shot of the lead.

After beginning day three tied first with Johnson, Ryan Moore slid into fourth after carding a round of 70.

Graeme McDowell shot a 71 with just a birdie on the 12th hole breaking the pattern of claiming par on every hole for the Northern Irishman, who sits on -2. 

Scotsman Martin Laird carded 69, placing him at fifth on nine under for the tournament, along with Sean O'Hair, Jimmy Walker and Chris Kirk.

In a stand-out moment from day three Laird, who is four shots of the lead, managed to sink an 83-foot putt to eagle the eighth.

Johnson is chasing his first win since 2015, while victory would be a tour first for Landry.