Si Woo Kim extended his lead at the Texas Open to four shots with the help of an ace in the second round of the Valero Texas Open, with Graeme McDowell the best of the Irish. 

Kim made an ace at the par-three 16th as well as birdies at the fifth, eighth, 12th and 14th in his bogey-free round of 66 to stand at 12 under to open up a healthy lead over six players who are tied for second, including Jordan Spieth and Ricky Fowler.

McDowell moved up two places to be tied in 15th place after posting another round of 69 to leave him six shots behind the leader.

Padraig Harrington just made the cut on one under after his round of 71, but there was disappointment for Seamus Power after he posted a 77. That left him on one over, two shots outside the cut mark.  

South Korea's Kim, 23, held a narrow one-shot lead overnight following his first-round 66 at TPC San Antonio.
American pair Harold Varner III and Adam Schenk leapt up the leaderboard after they both carded rounds of 66 to join former world number one Spieth, Fowler, Canada's Corey Conners and South Korean Kyoung-Hoon Lee in second place.

Spieth matched his first-round score of 68 with the help of an eagle and five birdies, but he also bogeyed the first, 10th and 12th holes.

Fowler, at one stage tied for the lead, has also produced consecutive rounds of 68, with an eagle and five birdies checked by three bogeys of his own, two of those at the 15th and 16th.