Ayrshire, Scotland (My Sportsbook) - Bruce Vaughan shot an even-par 71 on Friday to take sole possession of the lead midway through the Senior British Open Championship.

Vaughan, who shared the first-round lead with Eduardo Romero, was through 36 holes at three-under 139 for a one-shot cushion on John Cook. It marked the first time the 51-year-old Kansan held the second-round lead on the Champions Tour.

"I'm not at all nervous," said Vaughan, looking for his first over-50 win. "Shoot, there's still two days left."

Cook, the 11-time PGA Tour winner who claimed his first Champions Tour victory last year, also posted a 71 on Friday to remain one shot behind Vaughan at two-under 140.

"I'm as happy as can be," Cook said after a round of two birdies and two bogeys.

Defending champion Tom Watson, who has won three of the last five Senior British Opens, was still two off the lead after an up-and-down 71 that put him in a tie for third place with Bernhard Langer (71) and Romero (73) at one- under 141.

Mark McNulty (72) and Kirk Hanefeld (73) were the only other survivors to par at even-par 142.

Greg Norman, after his surprising showing in the British Open last week, remained in the hunt for his first senior major championship after shooting a 72 on Friday that left him eight shots off the lead.

It's a lot of strokes to make up, but Norman was happy with his play.

"I actually felt like I hit the ball really well today," said Norman, 53. "I felt like I played better today than I have in the last four or six tournaments."

Norman said he was close to making a decision about whether or not he would accept an invitation to next month's PGA Championship.

"I've almost made up my mind," he said. "I won't make a decision until late Monday night."

As for this week, host course Royal Troon is giving the "old people" (Watson's words) fits. The consensus was that it's set up fairly, if a little long, although there were only seven players at even-par or better.

"It gets fast and it kind of gets away from you a little bit and you have to be careful to hit quality shots and be very efficient," said Vaughan, who posted two birdies and two bogeys on Friday. "I feel like I've done that so far. We just have to see what this weekend gives us."

Vaughan rebounded from a bogey at the third hole with a birdie at the fourth, despite aggravating an injured knee.

"I stepped down on it the wrong way and it's hurting," said Vaughan, who went on to make 10 straight pars before going bogey-birdie again at 15 and 16. "But it's just part of golf."

Also part of golf -- especially at British Opens -- is the struggle to avoid big numbers that can hijack an otherwise good round. Watson managed one such dodge Friday on the course where he won the 1982 British Open, escaping what could have been a huge number at the par-four 11th.

"I hit what I felt was a pretty good drive with a three-wood and it was the wrong club -- I guess should have hit driver -- and it ended up in a bush," Watson recounted. "I took an unplayable (lie), dropped it, hit a shot that looked like it was going out of bounds and it hit the top of a wall and caroms way off to the left of the green. I pitched up to 12 feet and I hole it for bogey.

"That was an old Watson hole from back in the 70s."

Watson, with his three Senior British Open wins in the last five years, is on course to possibly win his ninth British Open overall. He claimed five of them on the PGA Tour.

"I'm in position to do well in the tournament," said Watson. "If I keep it out on the course and keep it out of the 'others' in the scoring column, I might have a chance to win the tournament."

That same prospect had Vaughan more than a little delighted.

"It would mean a lot," Vaughan said of winning his first major championship. "I love coming over here and it just proves that I can play out here."

Cook, with zero major championships among his 11 PGA Tour wins, was also excited about the prospect of finally winning the big one. He counts the British Open -- either one -- as "very high on my list."

"Winning 11 times isn't chopped liver, but you have to accentuate that with a major or a couple," said Cook. "I had my chances and didn't convert unfortunately, so I feel a little incomplete."

The cut line fell at 10-over 152 with 71 players moving on to the weekend. Sandy Lyle and Gary Player were among those who missed the number.