Wales' Jamie Donaldson withdrew from the US PGA Championship on Friday before the second round got under way at a damp, overcast Oak Hill.
Donaldson, who struggled to a 10-over-par 80 on Thursday, cited a back injury for pulling out of the final major of the year and joined American Bo van Pelt on the sidelines, while two-time major winner Angel Cabrera, who also shot a 80 in the first round, withdrew during his second round citing a wrist injury.
Van Pelt, who also recorded an opening 80, withdrew with a hip injury immediately after completing his first round which had otherwise seen players take advantage of the soft conditions.
35 players broke par and leaders Jim Furyk and Adam Scott were both just one shot outside the course record with rounds of 65 which left them one clear of Lee Westwood and Canada's David Hearn.
Westwood was among the early starters on Friday as he looked to boost his chances of a first major title at the 63rd attempt, the 40-year-old quickly shaking off the disappointment of letting slip a two-shot lead going into the final round of last month's Open at Muirfield.
"Somebody was asking me the other day, 'Does it get you down and do you get stressed when people go on about not winning a major championship?"' Westwood said after a flawless opening 66.
"I said, no, you really don't get stressed about golf anymore. I've played golf for 20 odd years out here on the best courses in the world and I get up every day and go and do something that I love.
"Golf doesn't stress me or disappoint me very often anymore. In fact I can't remember the last time it did. Just get on with it and just realise how lucky you are."