Trevor Immelman of South Africa birdied the last two holes to post his second four-under-par 68 and grab a one-stroke lead midway through Friday's second round of the U.S. Masters.

Immelman, overnight co-leader with Briton Justin Rose, matched his first-round score by posting three birdies on the back nine as he got hot with his putter on a warm, breezy day at Augusta National.

"It feels great to break 70 both rounds," said Immelman, 28, who has rebounded from serious illnesses in the past year.

"My play wasn't as sharp as yesterday but I holed some unbelievable putts out there. That always helps the scorecard."

Second on the leaderboard at seven-under-par was American Brandt Snedeker, who mirrored Immelman's rousing finish with birdies at 17 and 18 to complete a 68 for a 137 total, two shots better than compatriot Steve Flesch.

The left-handed Flesch posted the low round of the tournament so far by going five-under on the par-fives in a bogey-free 67.

Rose, playing in the final grouping of the day, was just teeing off behind a threesome including world number one and four times champion Tiger Woods, who shot even-par 72 in the opening round to stand four strokes back.

Flesch birdied holes number two, eight and 15, and had an eagle at the 13th where his three-iron from 234 yards finished a couple of feet from the hole.
   
"The fives is where I can take advantage," said Flesch, a relatively short hitter off the tee, who twice laid up to hit wedges in and twice went for greens in two.

Joining the 27-year-old Rose at four-under were Canadian Ames, who shot his second 70 for 140, twice winner Phil Mickelson, through 12 holes, and Briton Lee Westwood (10).

World number two Mickelson, who carded 71 in the first round, sank short birdie putts at the second and third holes and then put a flop shot over a mound off the eighth green to 10 feet and rolled it in for another birdie.

Snedeker, 27, drew a huge roar from the gallery at number six when he used his imagination by playing a chip at a 90-degree angle from the cup and watched the ball trickle down a slope and into the hole for birdie.

Immelman told reporters he could hardly imagine this start in the year's first major considering an intestinal problem that saw him lose more than 20 pounds last year and surgery at the end of last season to remove a benign tumour behind his rib
 cage.

"It's a thrill to play well here," he said.