EDMOND, Okla. — Colin Montgomerie thought it would be tough to keep his advantage from the first round at the U.S. Senior Open, and it was.

The Scotsman shot an even-par 71 on Friday and leads Scott Dunlap by one stroke after the second day of the tournament.

Montgomerie opened with a 65 on Thursday, and then held off the field in mid-90s heat and high humidity. He is at 6 under after two rounds.

“It’s not easy to repeat a good round as yesterday’s was, but this was as good, to be honest,” he said. “Seventy-one out there was a good effort. Breezy conditions, windier than it was yesterday, warmer and with the pack coming at you — it’s never easy.”

Dunlap had a 69 in the first round and a 68 in the second to get to 5 under.

He was at 2 under after starting on the back nine, and then went back to the front nine and birdied Nos. 2, 5 and 7 on his way to a 32.

“I have been particularly good with the putter this week,” Dunlap said. “Been tidy. I have made a couple, made all my short ones. You know, those will be big in any tournament, for sure, but especially a major.”