Bet with caddie behind Chun's British Open charge

Professional golfers often vie for fat paycheques but it is a much smaller prize that is fuelling South Korean Chun In-gee's drive for a maiden Women's British Open crown and a fourth major title.

Chun shot a five-under 66 in the second round at Muirfield on Friday for a one-stroke tournament lead, an inspired showing that had its roots in a bet she had with her caddie.

"Before I started the tournament, my caddie Dean and I spoke about the course and after that, we had a little bit of a bet," Chun told reporters.

"If I make the bogey-free round, he said he's going to buy dinner and pay me like $100 for each day if I can make it."

The 27-year-old made two bogeys in the opening two rounds but added she was determined to set that right over the weekend.

"Before I start the round, I always set another goal to make a bogey-free round," said Chun. "I think that mindset helped a lot on the course."

Swede Madelene Sagstrom and South Africa's Ashleigh Buhai are tied for second at seven-under heading into Saturday's third round.