A week after Korea's K.J. Choi ran away with the Compaq Classic title in New Orleans, Maruyama built a two-shot lead over Jim Carter and Paul Stankowski at 10-under 130, moving closer to his second win in 90 PGA Tour starts.
Maruyama won in Milwaukee last year and, like Choi, has grown more comfortable in the United States, recording a pair of top-10 finishes in his last six starts. He tied for fourth six weeks ago in Houston.
There have been just three Asian winners in PGA Tour history. Japan's Isao Aoki was the first, claiming the 1983 Hawaiian Open.
Carter, who has just three top-10 finishes the past four seasons, followed a 65 with a 67 to tie Stankowski for second at 132. Stankowski has just one top-10 finish in 2002.
Tiger Woods, returning to the tour for the first time since his third Masters triumph, got back into contention with a 65. He opened with a 1-over 71 but is just six strokes back at 136.
The first two rounds of the tournament were played on two courses -- the host TPC Four Seasons Resort Las Colinas and Cottonwood Valley. Both are par-70s.