(Reuters) - Britain's Brian Davis upstaged some of golf's biggest names as he charged into a share of the early second-round lead at the weather-hit Houston Open in Humble, Texas on Friday.

The 37-year-old Englishman, who has recorded five runner-up finishes on the PGA Tour without yet winning a title, fired a flawless seven-under-par 65 at the rain-softened Redstone Golf Club.

One of 93 players who had to complete the opening round earlier in the day, Davis birdied two of his last four holes to finish level on 11-under 133 with South African Louis Oosthuizen (66).

Defending champion Phil Mickelson, joint leader after the first round, bogeyed his final hole for a 70 to lie two off the pace along with fellow Americans Tommy Gainey (67) and JB Holmes (67) as well as Briton Greg Owen (69).

Three-times major winner Ernie Els, who needs to win the Houston Open to qualify for next week's Masters, was at five-under 139 after shooting a 69.

Davis was delighted with his performance after struggling for form on the PGA Tour earlier this season.

"It was a good day at the office today," the Englishman told reporters, having played 32 holes on Friday after first-round action was suspended on Thursday when thunderstorms swept across Redstone.

"I played some good golf and obviously put myself into position for the weekend."

More than an inch of rain saturated the course on Thursday and tournament organisers allowed the players to lift, clean and replace their balls in the delayed second round.

SPONSOR'S EXEMPTION

Davis, who tied for fourth at last week's Arnold Palmer Invitational after being given a sponsor's exemption, felt he was finally benefiting from various changes he made to his game at the end of last year.

"I changed caddies, sports psychologist and worked on getting my swing back where I want it to be, to improve it as well but get rid of the faults I had," he said.

"I felt really good coming out to start the season and I played awful. It's one of them things you got to stay the course and keep at it. It's been getting better, and obviously a couple of good rounds here."

Mickelson, who completed an eight-birdie 65 earlier in the day to join Swede Carl Pettersson and Argentina's Angel Cabrera in a share of the first-round lead, did not score as well in the afternoon.

"I wasn't quite as hot with the putter," the American left-hander said. "I had a lot come close but not quite go in.

"I played pretty well in the second round, but I didn't get the score that I had hoped. I got to light it up on the weekend."

The weather-delayed second round was likely to spill over into Saturday when the cut is projected to fall at two under.

Among those likely to miss out were South African Charl Schwartzel, who will defend his Masters title at Augusta National next week, and British Open champion Darren Clarke of Northern Ireland.

(Reporting by Mark Lamport-Stokes in Los Angeles; Editing by Nick Mulvenney)

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