* Four players share halfway lead
* Only three players break par in second round
* More than 100 balls end up in the water (Adds quotes, detail)
By Steve Keating
DORAL, Florida, March 7 (Reuters) - American Hunter Mahan eagled his penultimate hole to grab a share of the halfway lead at the WGC-Cadillac Championship on Friday as the Blue Monster showed its true colours, with more than 100 golf balls ending up in the water.
On a gruelling day that some players described as a survival test, Mahan eagled the par five eighth in fading light for a second round of two-over 74 that left him tied for the lead with his compatriots Dustin Johnson (74), Patrick Reed (75) and Matt Kuchar (74) at one-under par.
Northern Irishmen Rory McIlroy (74) and Graeme McDowell (71), Italian Francesco Molinari (75) and Welshman Jamie Donaldson, who posted the low round of the day with a two-under 70, were all lurking one shot further back.
"I felt stressed all day because I knew every shot had a big penalty written all over it, staring at bogey or worse I thought at a well struck shot," Mahan told reporters. "It was a really tough day.
"There wasn't an easy shot out there and you know, you're going to have to find a way to make some putts.
"One of those rounds where it could go south pretty fast so you've got to grind it out and find a way to get a number up there and get to the weekend."
Long regarded as one of the PGA Tour's great layouts, the Blue Monster course underwent a massive $251 million renovation that made it even more frightening and almost unplayable when the winds whipped across the sprawling layout on Friday.
With most players arriving early to complete their rain-delayed opening rounds, exhausted golfers slumped off the course after a day of battling brutal winds and fatigue.
Only three players managed to break par during a wild second round that saw 113 balls find a watery grave while the average score was four-over 76.
"It was just brutally difficult," said McDowell. "I don't think I've played in conditions this difficult in the U.S..
"It's an Open Championship day. It's a real Friday afternoon at St. Andrews in 2010 before they called it.
"It was hard out there, really, really hard, and part of me feels ecstatic to be off the golf course right now."
TOP RANKING SHOWDOWN
One of the intriguing sub-plots at the $9 million event was expected to be a showdown between world number one Tiger Woods and a Australian world number two Adam Scott for top spot in the rankings.
Scott could have a chance to replace Woods as number one if he wins on Sunday but the two men have spent much of the opening two rounds slugging it out closer to the bottom of the leaderboard.
Woods, who had a blazing finish to his rain-delayed first round making three successive birdies before he gave a shot back with a bogey at 18, was quickly on the charge in the afternoon.
The 14-time major winner carded birdies on his opening two holes but was soon sliding back down the leaderboard with four bogeys.
The highlight for the round came on the fourth when Woods rolled in a massive 92-foot birdie putt which was followed by another birdie at the fifth but the fight back would end with four straight pars and a one-over 73 to sit on five-over.
"That was a tough golf course today," said Woods, who found the water three times during the second round.
"I don't think that we expected the golf course to be that hard that fast, but it kept getting quicker and quicker."
Scott, who arrived on Friday sitting one shot off the lead at two-under, finished his opening round at three-over and continued to lose ground in the afternoon with a 73 to reach the midway mark at four-over.
Phil Mickelson, another former-champion, looked headed for trouble when he began his second round with a par and three consecutive double-bogeys before he scrapped his way to a 75 to join Woods on 149, six shots behind the leaders. (Editing by Julian Linden/Greg Stutchbury)