Story highlights Phil Mickelson raises hopes of a fourth Green Jacket after returning from injury

American four shots off the lead after opening round of Houston Open

He practiced at Augusta earlier this week ahead of season's opening major

His old rival Tiger Woods is missing the Masters, but three-time champion Phil Mickelson should be teeing off at Augusta next week after allaying fears about his fitness.

The veteran golfer pulled out during last week's Texas Open with a muscle problem, having missed the Farmers Insurance Open in late January with a back issue.

However, the 43-year-old raised hopes of claiming a career sixth major title after coming through Thursday's opening round at the Houston Open in good shape.

"I feel a lot better," Mickelson told the PGA Tour website. "I travel with a light therapy machine, and I got on it right away, and I think that made a world of difference as far as expediting the healing process to where it doesn't hurt anymore.

"It just feels sore like I was working out, as opposed to kind of a painful experience."

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Mickelson, the 2011 Houston winner, carded a bogey-free four-under-par 68 to be tied for 18th in a group including fellow veterans Ernie Els, Davis Love, Retief Goosen and 2012 U.S. Open champion Webb Simpson.

They were three shots behind leaders Bill Haas -- the PGA Tour's 2011 FedEx Cup champion -- and fellow American Charley Hoffman, seeking his first victory since 2010.

World No. 7 Rory McIlroy, another Masters title contender, was tied for 59th after a 70.

On Tuesday and Wednesday, fifth-ranked Mickelson spent time practicing at Augusta, where he wore the victor's fabled Green Jacket in 2004, 2006 and 2010.

"I was able to spend more time with short irons, chipping, putting as opposed to driving the ball, but even that was pretty good today," he said.

"I hit the ball well off the tee and didn't miss very many fairways."