"It feels great," the 57-year-old Forster said. "It was tough with a 2:30 tee time, because I had all night and all day today to think about [making the cut]. But once I got here, it was fine."
Forster, who carded two birdies, three bogeys and a double bogey, struggled off the tee, hitting just six of 14 fairways, including only two of his last six. But he finished with seven straight pars to to make the cut by two.
Joe Daley, a Champions Tour member who graduated from Plymouth Whitemarsh High, sank five birdie putts in a round of 70 that left him at 142 after 36 holes.
Rocco Mediate, at 5-under, is Allen's closest pursuer at 135. Mediate finished with 14 straight pars while shooting a bogey-free 67. Jeff Sluman, who also shot 67, is at 4-under 136 after missing an 8-foot par putt on the 18th.
Allen was short with his birdie putt on the last hole, ending his bid to match the U.S. Senior Open record of 62 by Loren Roberts at Prairie Dunes in 2006.
The 54-year-old Allen never won in 394 starts on the regular tour, but he has four victories since joining the Champions Tour four years ago, including the 2009 Senior PGA Championship.
He had top-10 finishes in the U.S. Senior Open in 2010-11 and tied for 33d last year. His game has been on the upswing lately. He won the Mississippi Gulf Resort Classic in March and came to Omaha with three top-10 finishes in his last four events.
It looked as if Allen and Mediate would match birdies early. Mediate had three in four holes to start the afternoon and took a brief lead.
But Allen, playing in the group behind him, got on a tear. He hit every green in regulation while going out in 30 and made the turn with a 3-shot lead.
Allen's strength is his irons, and he was hitting them pure on the front nine, seemingly oblivious to the southerly winds gusting to 25 m.p.h. and the course's elevation changes.