A Baggy Green cap worn by former Australian Test cricket captain Allan Border was sold to a mystery buyer at auction on Thursday evening for almost $29,000.

The first of Border's Test caps to be put on the market went to a telephone bidder.

The managing director of Leskie Auctions, Charles Leskie, says Border exchanged the cap with a Western Australian collector for Don Bradman memorabilia.

Mr Leskie says it was one of four Baggy Greens auctioned last night, and definitely the most popular.

"Any Baggy Green is a great item for us to have for auction but an ex-captain and especially a captain as beloved and successful as Allan Border - it doesn't come up very often so there's been a lot of interest in this," he said.

"We've quite a large collection of Allan Border's cricketing memorabilia.

"He exchanged it with a collector in Western Australia who had some Don Bradman memorabilia that he wanted and they did a swap."