WEST DES MOINES, Iowa (AP) -- If R.W. Eaks can still play like he did on Friday, imagine how well he could do on a new pair of knees.

Eaks, told by doctors last month that he'll need replacements for both of his knees, shot a 5-under 66 and tied with Lonnie Nielsen for the lead after opening-round play at the Principal Charity Classic on Friday.

Joey Sindelar, Tom Purtzer, Kirk Hanefeld and Mark McNulty were one stroke back at 4-under 67. Loren Roberts, who finished second at Glen Oaks in 2006, was at 3-under along with Clarence Rose.

Eaks had been bothered by pain since last October. After looking first at his back and hips, doctors finally pinned Eaks's troubles on his ailing knees. But Eaks vows to keep playing until they finally give out, and Friday's round was a sign that he might be ready to snap a seasonlong slump.

Eaks finished tied for eighth in his last event, the Regions Charity Classic, but that's his only top-10 finish in 2008. Eaks won twice and finished sixth on the money list in 2007.

"I'm going to try to play as much I can for as long as I can before I do this," Eaks said of his impending knee surgeries.

Eaks took his only bogey on the 17th hole, and he found himself in the bunker on the final hole after missing the fairway. But Eaks muscled a 7-iron from about 160 yards out to within 4 feet of the pin for the birdie -- a shot made all the more remarkable by the fact that Eaks has hardly any strength left in his legs.

He made up for it with his putter, tying for the fewest of the day with just 24.

"I've accepted it now, and I've just got to make the best of what I can do," said Eaks, who has undertaken a strenuous lower-body regiment to try and get his legs back under him. "I'm doing whatever the doctors and the guys in the trailer tell me to do. If they tell to go home, I'm going home."

Nielsen, an Iowa native and former all-Big Ten golfer for the Hawkeyes, strung together three straight birdies on his front nine and birdied his final hole to pull into a tie for the lead. The highlight of Nielsen's day came on the par-3 5th hole, when he nailed a 50-foot downhill putt for birdie.

Nielsen hit 15 greens in regulation and followed those up with a strong day with his putter.

"My birdie putts all kind of looked the same, and darned if I didn't make quite a few of them," Nielsen said.

Roberts' last trip to Glen Oaks ended with heartbreak on the final two holes. They bit him again Friday, as he fell out of the lead with bogeys on both.

After shooting wide of the fairway on No. 17, Roberts hit a strong third shot that set up a decent par putt, which he missed. He then misfired on a par putt on the 18th hole.

In 2006, Roberts blew a two-shot lead just two holes from the finish, double-bogeying No. 17 and missing a 9-foot putt on the 18th that would have forced a playoff with Gil Morgan.

Denis Watson, who along with Scott Hoch is the only two-time winner in 2008 in the field, is at 2-under. Defending champion Jay Haas, who will take over first place in the points standings with a top-10 finish, shot a 1-under 70.

Hoch shot a 1-over 72 and is tied for 47th.

The start of play was delayed by nearly two hours after torrential downpours soaked the course on Thursday night and Friday morning. The weather had cleared up by the time the golfers teed off, though the lift, clean and place rule was in effect for balls in the fairway. Forecasters are predicting sunny skies and warm weather for the second and third rounds.

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