Updated

Michael Allen fired a 7-under-par 63 at the U.S. Senior Open Championship on Friday and grabbed a 5-stroke lead through two rounds, the largest margin in tournament history.

Allen was one of seven co-leaders after the first round, but he created unprecedented distance on Friday by tying for the second-lowest round in event history and moving to 10-under-par 130, which marks the lowest-ever 36-hole score at the U.S. Senior Open.

"I got off to kind of a slow start this year. My putting has been pretty inconsistent but right now I feel like I'm playing pretty well," said Allen. "I prepared well so I feel good. I'm enjoying the competition."

Rocco Mediate shot 67 and moved into second place at 5-under 135, one shot ahead of Jeff Sluman, who also carded a 67 at Omaha Country Club.

Former champion Fred Funk was tied for the first-round lead, but he dropped into a share of fourth place after Friday's 70. The 2009 winner was joined at 3-under by Jeff Brehaut, who shot 68.

Tom Lehman (71) and Mark O'Meara (71) are tied for sixth at 2-under, while Duffy Waldorf (69) and Gary Koch (68) share eighth at minus-1.

Fred Couples (69), Steve Elkington (70), Kenny Perry (73), Esteban Toledo (69), Tom Watson (70) and Peter Fowler (70) are tied for 10th at even-par 140.

Mediate appeared game to challenge Allen early Friday, notching three straight birdies from the second to briefly take the lead. But he couldn't maintain the pace, closing with 14 consecutive pars as the 2009 Senior PGA Champion set about building his historic lead.

Allen started strong as well with birdies at five of his first eight holes during an outward 30, capped by a gain at the eighth, where the 54-year-old dropped a 4-iron from 210 yards within 15 feet and drained the ensuing putt.

Around the turn, Allen stumbled to a bogey at the 12th, but he recovered with a birdie at No. 13, then highlighted his sparkling round with an eagle at the next.

Allen was on the green in two at the par-5 14th, but more than 50 feet remained between his ball and the cup. Long putter in hand, the four-time Champions Tour winner sent his eagle effort over the green's tiered ridge and raised his hands in disbelief as the ball tracked the hole, caught the back lip, then bounced up and in.

"It wasn't about me, something else happened," said Allen, pointing skyward. "It was nice it went in and it was kind of out of my control.

"I could hit that putt 100 times and not get it within five feet, I guarantee you. I hit a good putt, I did what I was trying to but, but then it went in."

After three straight pars, Allen needed a birdie at the last to match Loren Roberts for the lowest round in tournament history, but he 2-putted from 20 feet, settling for par and a comfortable 5-stroke lead.

NOTES: Roberts shot 62 at Prairie Dunes Country Club in 2006 ... Allen is coming off a tie for fourth at the Senior Players ... This marks the first time he has led at the halfway point of a major championship on the Champions Tour... Allen's 5-stroke lead is the largest 36-hole lead in a senior major since Hale Irwin was up by seven strokes through two rounds at the 1997 Senior PGA Championship. Funk set the scoring record of 20-under par when he won in 2009 ... A total of 64 players made the cut, which came at 5-over-par 145. Doug Hanzel was the lone amateur to make it through to the weekend.