Mickelson in the mix at Houston
Phil Mickelson (L) of the United States talks with his caddy Jim Mackay during round one of the Shell Houston Open at the Golf Club of Houston on April 3, 2014 in Humble, Texas - by Scott Halleran
Mickelson said the injury to his right oblique muscle, which had forced him to withdraw from the Texas Open last week, had responded well to treatment.
"I feel a lot better four or five days later," Mickelson said. "It doesn't hurt anymore. It just feels sore as opposed to a kind of painful experience."
Mickelson enjoyed his day at the Golf Club of Houston, where playing partner Keegan Bradley fired a 66 to share the early lead with fellow Americans Matt Kuchar and J.B. Holmes.
Bradley, Mickelson and the third man in their group -- former US Open champion Webb Simpson, all played without a bogey, Simpson also posting a 68.
"It was the first time I remember that happening, certainly in my career," Mickelson said. "Not to have any bogeys in the group is pretty special."
The group teed off on 10, and Bradley, a former US PGA Championship winner who notched a runner-up finish at Bay Hill last month, nabbed his first birdie of the day at the 13th, then added three in a row from the 15th.
"I hadn't been making any putts, and it seems like the putter just kind of woke up right about now, which is really a good time of year for it to do that," said Bradley, who is among the top players in the field using this tournament to hone their games for the first major of the year, the Masters at Augusta National next week.
With afternoon starters, including Northern Ireland's Rory McIlroy, still on the course, Bradley, Kuchar and Holmes had a one-shot clubhouse lead over four players -- Stewart Cink, Michael Thompson, Ben Curtis and Camilo Villegas.