Rory McIlroy and partner Shane Lowry shot an eight-under-par 64, leaving them six off the pace as they began the defence of their Zurich Classic title. In his first competitive round since winning the Masters and completing the career Grand Slam, McIlroy struggled on the opening nine, but improved after the turn. The Irish pair trail Isaiah Salinda and Kevin Velo, who fired a 58. Collin Morikawa and Kurt Kitayama are in a strong position. The reigning champions have never successfully defended the title.