* Lowry birdies two of last four holes * Shoots a 65 for commanding lead * Landry and Johnson tied for second (Adds detail, quotes) By Mark Lamport-Stokes OAKMONT, Pennsylvania, June 19 (Reuters) - Irishman Shane Lowry tightened his grip on the U.S. Open by seizing a four-shot lead when the weather-delayed third round was finally completed on a sun-splashed Sunday morning at Oakmont Country Club. Two ahead overnight in the second major championship of the year, Lowry birdied two of his last four holes to get to seven-under 203 with a first grand slam title looming in his sights. "It was a really good morning's work for me and I am really looking forward to getting out there in the afternoon and seeing what I can do," said Lowry, who won the biggest title of his career at the 2015 WGC-Bridgestone Invitational. More...